Columbia  ©nibersfitp 
intfjcCttpofi^etogorfe 

College  of  ^{jpsitciansi  anir  ^urgconjs 


Reference  ilititarj> 


BY  THE  SAME  AUTHOR 

'  THE     HISTOLOGY    AND     PATHO-HISTOLOGY     OF     THE     TEETH     AND 
ASSOCIATED   PARTS,"    I903. 

'  DENTAL     MICROSCOPY,"     A     HANDBOOK     OF     PRACTICAL    DENTAL 
HISTOLOGY." 

ist  Edition,  1895. 
2nd  Edition,  1899. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/introductiontodeOOhope 


AN   INTRODUCTION 


DENTAL    ANATOMY 


PHYSIOLOGY 


/ 


DESCRIPTIVE   AND   APPLIED 


ARTHUR    HOPEWELL-SMITH 

L.R.C.P.  LoND.,  M.R.C.S.  Eng.,  L.D.S.  Eng. 

JOHN   TOMES   PRIZEMAN   OF   THE   ROYAL   COLLEGE    OF   SURGEONS    OF  ENGLAND;    LECTURER   ON   DENTAL 

ANATOMY  AND  PHYSIOLOGY,  DENTAL  SURGEON,  AND  DEMONSTRATOR  OF  PRACTICAL  DENTAL 

HISTOLOGY-    AT    THE    ROY'AL    DENTAL    HOSPITAL    OF    LONDON;   MEMBER    OF    THE 

FACULTY   OF   MEDICINE    OF   THE    UNIVERSITY   OF   LONDON;    FELLOW 

OF    THE    ZOOLOGICAL    SOCIETY    OF    LONDON;    MEMBRE  / 

HONORAIRE    DE   LA    SOCIETE    ODONTOLOGIQUE  / 

DE    FRANCE;    KORRESP.    MITGLIED   DES  / 

CENTRAL-VEREINS  DEUTSCHER 
ZAHNARZTE,    ETC. 


WITH    340   NEW  AND  ORIGINAL  ILLUSTRATIONS,   INCLUDING  A   FRONTISPIECE 
IN    PHOTOGRAVURE  AND  5   PLATES 


LEA    &    FEBIGER 

PHILADELPHIA    AND    NEW   YORK 

1913 


p-2--  '  - 


(The  right  of  reproduction  of  the  Original  Illustrations 
is  strictly  reserved.) 


Entered  according  to  the  Act  of  Congress,  in  the  year  1913,  by 

LEA  &  FEBIGER 
in  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved. 


PREFACE 


An  attempt  has  been  made  in  the  following  pages  to  place  before  the  reader  a 
short  account  of  the  Essentials  of  Dental  Anatomy  and  Physiology,  and  in  conso- 
nance with  the  requirements  of  a  utihtarian  age,  to  indicate  those  aspects  of  such 
a  subject  which  may  have  some  direct  practical  bearing  upon  the  science  and  art 
of  Dental  Surgery.  Odontology  is  a  matter  of  fundamental  importance  to  one  who 
has  entered,  or  who  is  about  to  enter,  upon  the  practice  of  this  special  branch  of 
the  treatment  of  disease.  Hence  it  is  important  to  decide  what  is  necessary  for 
the  student  to  know,  that  he  may  be  able  to  deal  intelligently  and  intellectually 
with  every  phase  of  his  adopted  profession  as  he  encounters  it  during  his  life's  work. 

A  further  endeavour  has  been  made  to  endow  an  admittedly  unattractive  topic 
with  some  degree  of  interest,  and  to  create  in  the  mind  of  the  reader  an  atmosphere 
of  regard  which  the  contemplation  of  the  Anatomy  of  the  Teeth  deserves  and 
demands.  Surely  even  a  halo  of  romance  can  be  found,  if  looked  for,  in  this  study, 
so  closely  is  it  interwoven  with  the  Natural  History  of  Man  and  animals  on  this 
planet.  Human  teeth  have  been  imperishable  structures — when  not  affected  by 
disease — from  countless  ages;  and  their  physical  characters  and  enduring  natures 
have  been,  are,  and  may  be  able  to  render  them  of  the  greatest  value  in  medico- 
legal cases  in  which  much  happens  to  be  involved. 

As  an  occasional  means  of  identification  of  the  illustrious  dead,  c.  g..  Louis 
XVII  of  France,  and  the  Prince  Imperial,  son  of  Napoleon  III,  killed  by  the 
Zulus  in  1879,  or  the  victims  of  great  calamities,  such  as  extensive  fires,  Hke  that 
of  the  Bazar  de  la  Charite  in  Paris  in  1897.  the  teeth,  when  exhibiting  the  results 
of  surgical  interference,  have  been  found  to  be  of  enormous  importance;  in  criminal 
cases  their  similar  silent  testimony  may  prove  or  disprove  a  legal  argument;  in 
the  remains  of  prehistoric  man  they  afford  a  clue  to  the  nature  of  the  food  which 
supported  hfe  in  those  far-distant  ages;  and  in  indicating  the  habits  of  the  indi- 
vidual of  whose  body  they  form  a  part,  they  may  reveal  the  higher  qualities  or 
the  baser  constitution  of  his  mental  attributes. 

From  a  strictly  scientific  point  of  view,  also,  the  modern  zoologist,  appreciating 
the  value  and  importance  of  the  dental  armaments  of  the  vertebrates,  has  emplo}"ed 
some  of  their  main  features  for  the  purpose  of  classifying  and  arranging,  in  their 
proper  positions  in  the  scheme  of  Natural  History,  several  orders  of  mammals, 
such  as  the  rodents,  the  whales,  and  the  marsupials. 


vi  PREFACE 

Of  Sir  Richard  Owen  it  is  said  that,  given  a  single  fossilized  tooth,  he  could 
reconstruct,  with  considerable  accuracy,  the  main  skeletal  features  of  its  owner, 
whether  bird,  beast,  or  fish. 

.s  In  short,  teeth  take  their  allotted  place  in  Nature  as  do  the  other  parts  of  the 
anatomy  of  Man,  and  on  these  grounds  alone  should  be  deemed  worthy  of  con- 
sideration, attention,  and  investigation. 

The  mission  of  this  book  is  to  explain  how  it  comes  about  that  Man  has  a  certain 
number  of  teeth,  to  describe  their  functions — combined,  individual,  component — 
to  relate  the  method  of  their  implantation,  to  detail  their  growth  and  the  origin  of 
the  complexities  of  their  patterns,  and  to  narrate  the  role  they  play  in  the  economy 
of  Nature  generally,  and  their  close  association  with  other  portions  of  the  body. 

As  on  viewing  a  picture  for  the  iirst  time  one  stands,  or  should  stand,  at  a  dis- 
tance, to  apprehend  its  perspective,  and  inspect  its  composition  in  its  entirety, 
and  afterwards  approaches  closer  to  examine,  in  extended  detail,  its  several  por- 
tions, so  should  be  the  attitude  of  him  who  takes  up  this,  or  other  similar  volume. 
It  should  be  quickly  perused  from  cover  to  cover,  until  a  general  survey  of  the 
subject  and  the  meaning  of  the  arrangements  of  its  parts  is  understood.  Then 
each  portion  should  be  scrutinized,  and  studied  in  extenso. 

The  student  would,  therefore,  be  well  advised  to  read  the  pages  consecutively, 
not  a  passage  here  and  a  paragraph  there.  It  has,  of  course,  been  expedient  to 
divide  the  material  into  Chapters,  but  they  have  been  harmonized  in  such  a  manner 
that  each  is  dependent  upon  the  preceding,  and  cannot  possibly  be  thoroughly 
appreciated  without  a  knowledge  of  the  contents  of  its  predecessor.  Each  chapter 
anticipates  the  next,  and  leads  up  to  those  treating  of  the  Anatomy  and  the 
Relationships  of  the  Teeth  of  Man,  which,  in  the  author's  opinion  are  the  most 
important  of  the  whole  series. 

A  knowledge  of  the  elementary  principles  underlying  the  study  of  general  anat- 
omy, general  physiology,  and  biology  is  presupposed  and  actually  required;  the 
corollary  being,  therefore,  that  this  work  is  intended  for  the  use  of  the  senior  student 
and  practitioner.  Certain  chapters,  such  as  those  dealing  with  the  homologies 
of  the  Teeth,  the  development  of  the  mammalian  crowns,  the  influence  that  the 
Darwinian  theory  of  evolution  has  upon  the  teeth,  as  being  of  less  importance 
than  the  others,  have,  purposely,  been  treated  in  sketchy  outhne.  Descriptions  of 
the  minute  anatomy  of  the  dental  and  oral  tissues  have  been  designedly  omitted; 
for  information  regarding  them  references  should  be  made  to  the  Author's 
"The  Histology  and  Patho-histology  of  the  Teeth  and  Associated  Parts."  Com- 
parative pala2ontology  has  been  likewise  disregarded,  as  it  is  of  but  httle  moment 
in  relation  to  the  exercise  of  every-day  dental  work. 

It  would  seem  that  a  modification  of  some  of  the  expressions  commonly  made 


PREFACE  vii 

use  of  in  dental  parlance  is  imperative  and  necessary.  In  connection  with  the 
names  of  teeth,  the  "central"  incisor  should  be  invariably  known  as  the  "first" 
incisor,  the  "lateral"  as  the  "second"  incisor.  Similarly  the  word  "bicuspid" 
should  be  entirely  replaced  by  "premolar,"  and  it  is  at  once  obvious  that  the  terrns 
"six-year-old"  molar,  "twelve-year-old"  molar  and  "wisdom"  tooth  are  wrong. 
In  conformity  with  the  principles  and  teachings  of  Comparative  Anatomy  these 
teeth  should  be  recognized  as  the  "first,"  "second."  and  "third"  molars.  The 
"temporary"  should  always  be  styled  the  "deciduous"  dentition;  and  the  "articu- 
lation," the  "occlusion"  of  the  teeth.  Further,  it  is  evident  that  designations 
such  as  "open  bite,"  "edge-to-edge  bite,"  "underhung  bite,"  are  obsolete,  and 
that  it  is  desirable,  as  pointed  out  in  Chapter  XI,  to  change  them  to  "opharmosis," 
"prosharmosis,"  and  "epharmosis"  respectively. 

For  the  preparation  of  this  work  much  information  has  been  obtained  from 
examinations  of  the  specimens  in  the  Natural  History  Section  of  the  British  Museum, 
the  Odontological  Collection  of  the  Royal  College  of  Surgeons  of  England,  the 
Museums  of  the  Royal  Dental  Hospital  of  London,  Guy's  Hospital,  the  Univer- 
sities of  Cambridge  and  Birmingham,  the  Ecole  Dentaire  de  Paris,  the  Anatomische 
Anstalt  der  Universitat,  Berlin,  and  the  Pathologisches  Museum  der  Kgl.  Charite, 
Berlin. 

The  author  has  almost  essayed  "prendre  la  lune  avec  ses  dents."  If  he  has 
succeeded  in  his  task  of  merely  introducing  some  of  the  fascinating  facts  and 
theories  of  Dental  Anatomy  and  Physiology  to  the  younger  generation  of  students, 
his  attempt  will  be  justified. 

Portions  of  the  book  have  already  appeared  substantially  in  the  Transactions  of 
the  Fifth  International  Dental  Congress,  and  the  Second  Australian  Dental  Congress. 

In  connection  with  the  publication  of  the  volume,  the  author  owes  an  especial 
debt  of  gratitude  to  his  eminent  and  learned  friend.  Dr.  Edward  C.  Kirk,  for  his 
editorial  services,  so  readily  proffered  and  so  willingly  undertaken;  and  he  desires 
to  acknowledge  his  grateful  thanks  to  the  Publishers  for  the  extreme  care  they  have 
exercised  with  regard  to  the  typography  and  the  pictorial  aspect  of  its  pages. 

To  the  writings  of  Mr.  Chas.  S.  Tomes — whose  "Manual  of  Dental  Anatomy" 
is  well-known — of  Mr.  E.  Clodd,  Dr.  Black,  etc.,  he  is  greatly  indebted  for  very 
much  inspiring  and  interesting  intelligence.  Many  of  the  illustrations  are  from 
photographs  taken  by  Mr.  George  Payne,  Sub-Curator  of  the  Museum  of  the 
Royal  Dental  Hospital  of  London,  of  specimens  therein  found,  and  also  in  that 
of  the  Roj-al  College  of  Surgeons  of  England,  and  to  him,  and  to  the  authorities  of 
these  latter  institutions  he  is  beholden  for  much  kind  help. 

Park  Street.  P.ark  Lane,  London  W. 


CONTENTS 


CHAPTER    I 

The  Value  of  the  Study  of  Dental  Anatomy 

Introduction — Dental  Anatomy  the  Alphabet  of  Dental  Surgery — The  Utility  of  a 
Knowledge  of  its  Principles — The  Value  of  the  Study  of  Comparative  Dental  Anatomy 
— Problems  associated  with  the  Subject,  and  the  Need  for  their  Examination  from 
Various  Points  of  View — Scheme  of  Succeeding  Chapters,  culminating  in  Human 
Dental  Anatomy  Proper — Study  Completed  by  brief  Accounts  of  Dentitions  of  the 
Order  Mammalia. 

CHAPTER    II 

The  Teeth  and  their  Functions 

Definitions  of  Teeth  Generally — Kinds  of  Teeth — General  Major  Functions — The  Food 
of  Fishes,  Reptiles,  and  Mammals — The  Food  of  Man  in  Europe,  Asia,  Africa,  America, 
and  Melanesia — As  Factors  in  Facial  Development — The  Specific  Major  Functions 
of  Speech,  of  Ornamentation,  of  Emotional  Expression — The  Minor  Functions  of 
Prehension,  of  Sexual  Warfare,  of  Transport  and  Locomotion,  of  Offence,  of  the  Toilet, 
of  Chiselling,  of  Protection  from  Injury,  of  Sifting  Food,  of  the  Production  of  Sounds, 
and  of  Attack — Functionless  Teeth — Dental  Substitutes — The  Application  of  Nature 
to  the  Requirements  of  Art. 


CHAPTER    III 

General  Numeration  and  Topography 

The  Numbers  of  the  Teeth  in  Fishes,  Reptiles,  and  Mammals — Their  General  Osseous 
Relationships — Dental  Notations — The  Typical  Mammalian  Formula — The  Numerical 
Reduction  in  Man — Theories  Regarding  the  Incisors — The  Factors  in  the  Production 
of  the  Diminution  in  Number — Instances  of  Redundancy  and  Deficiency  in  Man. 


CHAPTER    IV 

The  Morphology  of  the  Teeth 84 

General  Considerations  Regarding  the  Shapes  of  Teeth — Examples  in  Fishes,  Reptiles, 
and  Mammals — Definitions  of  Individual  Teeth — Reasons  for  Morphological  Variations 
— "Adaptive  Modification"  as  Exemplified  in  Trigla  and  Lophius  Piscaloriiis,  in 
Viperine  Snakes  and  in  Marsupials — Definitions  of  Types  of  Collective  Dentitions. 


CONTENTS 


CHAPTER    V 

Darwiniana 103 

The  Origin  of  Variations  of  Species — History — The  Theories  of  Linnsus,  Cuvier,  Lamarck, 
Goethe,  and  Darwin — Natural  Selection — Sexual  Selection — Dental  Variations — 
Atypical  Dental  Heredity — Evidences  of  the  Mutability  of  Species — Proofs  of  Deriva- 
tion of  Species — Post-Darwinian  Theories — The  Mutation  Theory — Mendelism. 

CHAPTER    VI 

The  Implantation  and  Replacement  of  Teeth 125 

The  Implantation  of  Teeth  in  Fishes,  Reptiles,  and  Mammals — The  Replacement  of 
Teeth  in  Fishes,  Reptiles,  and  Mammals — Vertical  and  Oblique  Successions — Absorp- 
tions, Physiological  and  Pathological. 

CHAPTER    VII 

Dental  Homologies 132 

The    Meaning   of   Homology — Kinds   of   Homology — Examples — Meaning    of   Analogy — 
Difficulties  of  Homology — Examples. 

CHAPTER    VIII 

The  Evolution  of  the  Mammalian  Crowns 136 

The  Production  of  the  Complexities  of  Patterns  of  the  Mammalian  Crowns — The 
Concrescence  Theory;  Evidences  in  Favour — Examples — The  Tri tubercular  Theory 
— The  Work  of  Cope,  Osborn,  and  Wortman, 

CHAPTER    IX 

The  Teeth  of  the  Primates 146 

Introductory — The  Teeth  of  the  Lemnrs  and  the  Anthropoid  Apes — Prehistoric  Man — 
Rules  for  the  Descriptions  of  Mammalian  Dentitions — The  Dental  Index — The  Facial 
Angle — The  Gnathic  Index. 

CHAPTER    X 

The  Anatomy  of  the  Teeth  of  Man 174 

Introductory — General  Considerations — Descriptions  of  the  Permanent  Incisors,  Canines, 
Premolars,  and  Molars,  their  Measurements,  Variations  of  Mensuration,  Coronal 
Surfaces,  Necks,  Roots,  Dates  of  Calcification,  Pulp  Chambers  and  Root  Canals, 
Means  of  Identification  and  Surgical  Anatomy — The  Deciduous  Teeth — Age  Changes. 

CHAPTER    XI 

The  Relationships  of  the  Teeth  of  Man 228 

Their  Mutual  Association  with  the  Mouth  and  Osseous  System — The  Nervous  System — 
The  Vascular  System — The  Lymphatic  System. 


CONTENTS 


CHAPTER    XII 

The  Gingival  Region 250 

Introductory — Character  of  the  Bone  of  the  Alveolar  Sockets  of  the  Teeth  of  Man,  the 
Anthropoidea  and  the  FelidcB — Physiological  Absorption  of  Bone — The  Soft  Tissues — 
The  Gingival  Trough  and  its  Contents — The  Distribution  of  the  Glands  of  the  Gum. 

CHAPTER    XIII 

The  Development  of  the  Jaws  and  Teeth 263 

Early  Formation  of  the  Head  and  Face — Ossification  of  the  Maxillae — Of  the  Premaxillae 
— Changes  in  the  Maxillas  Produced  by  Age — Ossification  of  the  Mandible — Various 
Theories — Changes  in  the  Mandible  Produced  by  Age — The  Growth  of  the  Deciduous 
Teeth— The  Growth  of  the  Permanent  Teeth. 


CHAPTER    XIV 

The  Dynamics  of  Eruption  ....  

Introductory — Certain  Facts — The  Radicular  Elongation  Theory — Interstitial  Growth 
of  Bone — Deposition  of  Bone — Blood  Pressure — The  Epithelial  Theory — The  Guber- 
naculum — The  Influence  of  Nutrition — The  Dates  of  Eruption. 


CHAPTER    XV 


The  Functions  of  the  Dental  Tissues 

Introductory — The  Uses  of  Nasmyth's  Membrane — Of  the  Enamel — Of  the  Dentine- 
Of  the  Dental  Pulp — Of  the  Periodontal  Membrane  and  Cementum — Of  the  Gum- 
The  Sensitiveness  of  Teeth — Of  the  Enamel — Of  the  Dentine — Of  the  Cementum- 
Dental  Pain — Modifications  of  Sensation. 


CHAPTER    XVI 

Mammalian  Dentitions 314 

The  General  and  Dental  Characteristics  and  Variations  of  the  Teeth  of  the  Cheiroptera — 
Of  the  Insectivora — Of  the  Rodentia — Of  the  Carnivora — Of  the  Cetacea — Of  the  Sirenia 
— Of  the  Ungnlaia — Of  the  Edentata — Of  the  Marsupialia — Of  the  Monotremala. 


Glossary 355 

Appendix «■      •     357 


LIST    OF    ILLUSTRATIONS 


PLATES 

Plate 

The  Vascular  and  Nervous  Systems  of  the  Maxillas  and  Mandible  of  a 

Child.     X  f Frontispiece 

I.  Human  skull  in  norma  facialis.      X  -} To  face  page  174 

II.  Human  skull  in  norma  lateralis.      X  yff To  face  page  228 

III.  Human  skull  in  norma  basilaris.      X  I To  face  page  250 

IV.  Human  skull  in  norma  occipitalis.      X  y To  face  page  262 

V.  Human  mandible.      X  y To  face  page  286 


ILLUSTRATIONS   IN   THE   TEXT 


Fig 


1.  Tooth  erupted  in  the  nasal  fossa.     X  ^        23 

2.  Tooth  erupted  in  the  sigmoid  notch  of  the  mandible.      X  xV 23 

3.  Teeth  in  an  ovarian  teratoma.      X  i^ 24 

4.  Teeth  in  an  ovarian  teratoma.      X  -J-J 24 

5.  Radiograph  of  an  unerupted  canine 24 

6.  Radiograph  of  an  unerupted  canine 24 

7.  Diagram  of  a  cervical  tooth  of  a  sheep 30 

8.  Tooth  attached  to  the  wall  of  an  ovarian  teratomatous  cyst.      X  j         ■ 3° 

9.  Mouth  of  a  lamprey.      X  i 32 

10.  Palate  of  a  marine  gasteropod.      X  -f- 32 

11.  Radula  of  a  marine  mollusc.      X  -f" 33 

12.  Jaws  of  a  wolf-fish.      X  5- 34 

13.  Diagram  of  the  oral  parts  used  in  the  production  of  speech 44 

14.  Skull  of  a  native  of  East  Africa.     X  y 47 

15.  Ethnic  dental  mutilations — Type  I           50 

16.  Ethnic  dental  mutilations — Type  11         50 

17.  Ethnic  dental  mutilations — Type  III 50 

18.  Ethnic  dental  mutilations — Type  IV 50 

19.  Ethnic  dental  mutilations — Type  V         50 

20.  Ethnic  dental  mutilations — Type  VI 50 

21.  Jaws  of  a  pike.      X  i 52 

22.  Head  of  a  true  dolphin.      X  r; 52 

23.  Skulls  of  a  male  and  female  narwhal.     X  A 53 

24.  Skull  of  a  male  musk-deer.      X  i 54 

25.  Skull  of  a  beaver.      X  5 55 

26.  Skull  of  a  flying  lemur.     X  {'„ 57 

27.  Skull  of  a  porcupine.     X  I 57 


xiv  LIST  OF  ILLUSTRATIONS 

Fig.  Page 

28.  Skull  of  a  male  babirussa.     X  i 58 

29.  Rostrum  of  a  sawfish.      X  5 60 

30.  Head  of  hemiramphiis.      X  r 64 

31.  The  sea-horse.     X  i 65 

32.  Jaws  of  a  lung  fish.      X  i         65 

33.  Skull  of  a  monitor  lizard.      X  * 66 

34.  The  teeth  of  an  adult  man.      X  i      , 67 

35.  Skull  of  a  chimpanzee.      X  3 67 

36.  Skull  of  a  New  World  monkey.      X  I 68 

37.  Diagram  of  the  skull  of  a  fish 69 

38.  Jaws  of  a  ray.      X  i 70 

39.  Jaws  of  the  eagle  ray.     X  ^ 71 

40.  Maxillffi  showing  persistent  premaxillary  sutures.      X  to         76 

41.  Model  of  a  mouth  possessing  six  maxillary  incisors.      X  j% 76 

42.  Photograph  of  a  mouth  possessing  seven  maxillary  incisors 76 

43.  Radiograph  showing  absence  of  a  maxillary  second  incisor 78 

44.  Radiograph  showing  absence  of  the  corresponding  tooth 78 

45.  Radiograph  showing  absence  of  a  maxillary  canine 78 

46.  Radiograph  showing  absence  of  the  corresponding  tooth 78 

47.  Radiograph  showing  redundancy  of  the  mandibular  canine 79 

48.  Radiograph  showing  absence  of  the  same 80 

49.  Radiograph  showing  absence  of  the  mandibular  second  premolars 81 

50.  Radiograph  showing  absence  of  the  mandibular  second  premolars 82 

51.  Jaws  of  a  sheep's-head  fish.     X  | 85 

52.  Jaws  of  a  globe-fish.     X  H 85 

53.  Jaws  of  a  shark.      X  tV 86 

54.  Jaws  of  the  blue  shark.      X  4 86 

55.  Skull  of  Trichinrus.      X  j 87 

56.  Skull  of  a  crocodile.      X  tV      • 87 

57.  Skull  of  an  armadillo.     X  ^ 88 

58.  Skull  of  the  three-toed  sloth.      X  i 89 

59.  Jaws  of  the  Aard-vark.      X  \        89 

60.  Jaws  of  the  leopard  seal.      X  i 90 

61.  Molars  of  the  African  and  Indian  elephant.      Xi 91 

62.  Skull  of  a  hyaena.      X  | 92 

63.  A  trigla.      X  + 94 

64.  Jaws  of  a  python.      X  | 95 

65.  Poison  fangs  of  a  viper.      X  y 96 

66.  Skull  of  the  kangaroo.      X  i 97 

67.  The  carnivorous  type  of  dentition.      X  i 99 

68.  The  herbivorous  type  of  dentition.      X  i 100 

69.  The  insectivorous  type  of  dentition.      X  \ 100 

70.  The  omnivorous  type  of  dentition.      X  \ loi 

71.  Diagram  illustrating  "  correspondence  with  environment " 108 

72.  Protective  mimicry  in  insects.      X  to '15 

73.  Skulls  of  male  and  female  Old  World  monkeys.     X  4 116 

74.  Jaws  of  the  Port  Jackson  shark.      X  J 128 

75.  yisi.-a6ih\&  oi  Alepidosaurus  jerox.      X  f 129 

76.  Radiograph  of  the  normal  absorption  of  a  deciduous  molar 130 


LIST  OF  ILLUSTRATIONS  xv 

Fig.  Page 

77.  Radiograph  of  the  abnormal  absorption  of  a  deciduous  molar 130 

78.  Diagram  of  the  structure  of  the  arm,  leg,  and  wing 134 

79.  Radiograph  of  two  supernumerary  teeth  in  man 137 

80.  The  stages  of  trituberculism 139 

81.  The  homologies  of  the  cusps  of  a  maxillary  molar.      X  I         142 

82.  The  homologies  of  the  cusps  of  a  mandibular  molar.      X  | 142 

83.  Skull  of  a  lemur.      X  ^ 148 

84.  Skeleton  of  a  New  World  monkey.     X  2 149 

85.  Skull  and  jaws  of  a  baboon.     X  i 150 

86.  Skull  of  an  Old  World  monkey.     X  f 151 

■  87.  Chart  of  the  geological  epochs 153 

88.  Jaws  of  a  man  of  Britain,  dating  from  370  a.d.      X  |         158 

89.  The  same.      X  j 158 

90.  The  same.     X  f 159 

91.  Teeth  of  the  same.     XI 159 

92.  Skeletons  of  a  man  and  a  gorilla;  front  aspect.      X  y j 164 

93.  Skeletons  of  a  man  and  a  gorilla;  lateral  aspect.      X  t'i 165 

94.  The  diastema  in  the  maxillae  of  a  man  of  New  Guinea 169 

95.  Prognathous  skull  of  a  native  of  East  Africa.      X  5 170 

96.  The  facial  angle  of  a  dog 171 

97.  The  facial  angle  of  a  monkey 171 

98.  The  facial  angle  of  a  man  (European) 171 

99.  The  left  maxilla  and  mandible  of  a  man.      X  r 174 

100.  Vertical  section  through  the  maxilla  and  mandible.      X  i 175 

loi.  The  maxillary  first  Incisor — Labial  aspect.      X  x 178 

102.  The  maxillary  first  Incisor — Lingual  aspect 178 

103.  The  maxillary  first  Incisor — Mesial  aspect 178 

104.  The  maxillary  first  Incisor — Mesio-distal  section 178 

105.  The  maxillary  first  Incisor — Labio-lingual  section 178 

106.  The  maxillary  first  Incisor — Various  horizontal  sections 178 

107.  The  maxillary  second  Incisor — Labial  aspect.      X  y 18 

108.  The  maxillary  second  Incisor — Lingual  aspect 18 

109.  The  maxillary  second  Incisor — Distal  aspect 18 

no.  The  maxillary  second  Incisor — Mesio-distal  section iS 

111.  The  maxillary  second  Incisor — Labio-lingual  section 18 

112.  The  maxillary  second  Incisor — Various  horizontal  sections 18 

113.  Section  through  a  maxillary  Incisor  i»  5Jto.      X  t         182 

114.  The  maxillary  Canine — Labial  aspect.     X  t 184 

115.  The  maxillary  Canine — Lingual  aspect 184 

116.  The  maxillarjr  Canine — Mesial  aspect 184 

117.  The  maxillary  Canine — Labio-lingual  section 184 

118.  The  maxillary  Canine — Mesio-distal  section '     .  184 

119.  The  maxillary  Canine — Various  horizontal  sections 184 

120.  Section  through  a  maxillary  Canine  in  situ.      X  }         185 

121.  The  maxillary  first  Premolar — Distal  aspect.      X  | 187 

122.  The  maxillary  first  Premolar — Mesial  aspect 187 

123.  The  maxillary  first  Premolar — Buccal  aspect 187 

124.  The  maxillar}'  first  Premolar — Bucco-lingual  section 187 

125.  The  maxillary  first  Premolar — Mesio-distal  section 187 


xvi  LIST  OF  ILLUSTRATIONS 

Fig.  Page 

126.  The  maxillary  first  Premolar — Various  horizontal  sections 187 

127.  Section  through  a  maxillary  Premolar  in  situ.      X  I 189 

128.  The  maxillary  second  Premolar — Mesial  aspect.      X  t 190 

129.  The  maxillary  second  Premolar — Distal  aspect 190 

130.  The  maxillary  second  Premolar — Buccal  aspect 190 

131.  The  maxillary  second  Premolar — Bucco-lingual  section 190 

132.  The  maxillary  second  Premolar — Mesio-distal  section 190 

133.  The  maxillary  second  Premolar — Various  horizontal  sections 190 

134.  The  maxillary  first  Alolar — Mesial  aspect.      X  i 195 

135.  The  maxillary  first  Molar — Buccal  aspect 195 

136.  The  maxillary  first  Molar — Lingual  aspect  . 195 

137.  The  maxillary  first  Molar — Bucco-lingual  section 195 

138.  The  maxillary  first  Molar — Mesio-distal  section 195 

139.  The  maxillary  first  Molar — Various  horizontal  sections 195 

140.  Section  through  a  maxillary  Molar  m  iJte.      X  -j- ^ 198 

141.  The  maxillary  second  Molar — Mesial  aspect.      Xj 200 

142.  The  maxillary  second  Molar — Distal  aspect 300 

143.  The  maxillary  second  Molar — Buccal  aspect 200 

144.  The  maxillary  second  Molar — Bucco-lingual  section 200 

145.  The  maxillary  second  Molar — Mesio-distal  section 200 

146.  The  maxillary  second  Molar — Various  horizontal  sections 200 

147.  The  maxillary  third  Molar — Mesial  aspect.      X  x 202 

148.  The  maxillary  third  Molar — Buccal  aspect 202 

149.  The  maxillary  third  Molar — Distal  aspect 202 

150.  The  maxillary  third  Molar — Mesio-distal  section 202 

151.  Horizontal  sections  through  the  maxilla.      X  j 203 

152.  The  mandibular  first  Incisor — Labial  aspect.      X  I 206 

153.  The  mandibular  first  Incisor — Lingual  aspect 206 

154.  The  mandibular  first  Incisor — Mesial  aspect 206 

155.  The  mandibular  first  Incisor — Mesio-distal  section 206 

156.  The  mandibular  first  Incisor — Labio-lingual  section 206 

157.  The  mandibular  first  Incisor — Various  horizontal  sections 206 

158.  The  mandibular  second  Incisor — Labial  aspect.      X  r 208 

159.  The  mandibular  second  Incisor — Lingual  aspect 208 

160.  The  mandibular  second  Incisor — Mesial  aspect 208 

161.  The  mandibular  second  Incisor — Mesio-distal  section 208 

162.  The  mandibular  second  Incisor — :Mesio-distal  section 208 

163.  The  mandibular  second  Incisor — Labio-lingual  section 208 

164.  The  mandibular  second  Incisor — Various  horizontal  sections 208 

165.  The  mandibular  Canine — Labial  aspect.      Xt 210 

166.  The  mandibular  Canine — Lingual  aspect 210 

167.  The  mandibular  Canine — Mesial  aspect 210 

168.  The  mandibular  Canine — Mesio-distal  section 210 

169.  The  mandibular  Canine — Labio-hngual  section 210 

170.  The  mandibular  Canine — Various  horizontal  sections 210 

171.  The  mandibular  first  Premolar — Labial  aspect.      X  i 212 

172.  The  mandibular  first  Premolar — Lingual  aspect 212 

173.  The  mandibular  first  Premolar — Distal  aspect 212 

174.  The  mandibular  first  Premolar — Mesio-distal  section 212 


LIST  OF  ILLUSTRATIONS  xvii 

Fig.  Page 

175.  The  mandibular  first  Premolar — Labio-lingual  section 212 

176.  The  mandibular  first  Premolar — Various  horizontal  sections 212 

177.  The  mandibular  second  Premolar — Buccal  aspect.      XI 214 

178.  The  mandibular  second  Premolar — Lingual  aspect 214 

179.  The  mandibular  second  Premolar — Mesial  aspect 214 

180.  The  mandibular  second  Premolar — Mesio-distal  section 214 

181.  The  mandibular  second  Premolar — Bucco-lingual  section 214 

182.  The  mandibular  second  Premolar — Various  horizontal  sections 214 

183.  The  mandibular  first  Molar — Buccal  aspect.     X  ! 216 

184.  The  mandibular  first  Molar — Lingual  aspect 216 

185.  The  mandibular  first  Molar — Mesial  aspect 216 

186.  The  mandibular  first  Molar — Mesio-distal  section 216 

187.  The  mandibular  first  Molar — Bucco-lingual  section 216 

188.  The  mandibular  first  Molar — Various  horizontal  sections 216 

189.  The  mandibular  second  Molar — Buccal  aspect.      X  j 219 

190.  The  mandibular  second  Molar — Lingual  aspect 219 

191.  The  mandibular  second  Molar — Mesial  aspect 219 

192.  The  mandibular  second  Molar — Mesio-distal  section 219 

193.  The  mandibular  second  Molar — Bucco-lingual  section .219 

194.  The  mandibular  second  Molar — Various  horizontal  sections 219 

195.  The  mandibular  third  Molar — Buccal  aspect.      X  I 220 

196.  The  mandibular  third  Molar — Mesial  aspect 220 

197.  The  mandibular  third  Molar — Distal  aspect 220 

198.  The  mandibular  third  Molar — Mesio-distal  section 220 

199.  Horizontal  sections  through  the  mandible.      X  S 221 

200.  Changes  in  the  crowns  of  Molars  due  to  age.      X  -}? 221 

201.  Radiograph  of  the  left  maxilla  of  a  woman  showing  a  mal-placed  maxillary  third  Molar  .  221 

202.  The  maxillary  deciduous  first  Incisor — Labial  surface.      X  tJ 224 

203.  The  mandibular  deciduous  first  Incisor — Labial  surface.      X  ji         224 

204.  The  maxillary  deciduous  second  Incisor — Labial  surface.      X  \l 224 

205.  The  mandibular  deciduous  second  Incisor — Labial  surface.      X  I J 224 

206.  The  maxillary  deciduous  Canine — Labial  surface.      X  ]. 224 

207.  The  maxillary  deciduous  Canine — Lingual  surface 224 

208.  The  maxillary  deciduous  Canine — Distal  surface 224 

209.  The  maxillary  deciduous  Canine — Labio-lingual  section 224 

210.  The  maxillary  deciduous  Canine — Mesio-distal  section 224 

211.  The  mandibular  deciduous  Canine — Labial  surface.      X   | 224 

212.  The  mandibular  deciduous  Canine — Lingual  surface 224 

213.  The  mandibular  deciduous  Canine — Mesio-labial  surface 224 

214.  The  mandibular  deciduous  Canine — Labio-lingual  section 224 

215.  The  mandibular  deciduous  Canine — Mesio-distal  section 224 

216.  The  maxillary  deciduous  first  Molar — Distal  aspect.      X  1- 224 

217.  The  maxillary  deciduous  first  Molar — Mesial  surface 224 

21S.  The  maxillary  deciduous  first  Molar — Buccal  surface 224 

219.  The  maxillary  deciduous  first  Molar — Bucco-lingual  section 224 

220.  The  maxillary  deciduous  first  Molar — Mesio-distal  section 224 

221.  The  mandibular  deciduous  first  Molar — Buccal  surface.      X  ] 225 

222.  The  mandibular  deciduous  first  Molar — Lingual  surface 225 

223.  The  mandibular  deciduous  first  Molar — Distal  surface 225 


xviii  LIST  OF  ILLUSTRATIONS 

Fig.  Page 

224.  The  mandibular  deciduous  first  Molar — Mesio-distal  section 225 

225.  The  mandibular  deciduous  first  Molar — Bucco-lingual  section 225 

226.  The  maxillary  deciduous  second  Molar — Mesial  surface.      X  x 225 

227.  The  maxillary  deciduous  second  Molar — Distal  surface 225 

228.  The  maxillary  deciduous  second  Molar — Buccal  surface 225 

229.  The  maxillary  deciduous  second  Molar — Mesio-distal  section 225 

230.  The  maxillary  deciduous  second  Molar — Bucco-lingual  section 225 

231.  The  mandibular  deciduous  second  Molar — Lingual  surface.      X  f 225 

232.  The  mandibular  deciduous  second  Molar — Buccal  surface 225 

233.  The  mandibular  decidvious  second  Molar — Distal  surface 225 

234.  The  mandibular  deciduous  second  Molar — Mesio-distal  section 225 

235.  The  mandibular  deciduous  second  Molar — Bucco-lingual  section 225 

236.  Surface  markings  of  the  face 228 

237.  Diagram  of  a  section  of  the  buccal  cavity 229 

238.  Diagram  of  the  buccal  cavity 231 

239.  Diagram  of  types  of  palatal  arches 232 

240.  Occlusion  of  the  permanent  teeth  of  man.      X  js 234 

241.  Radiograph  of  the  normal  jaws  of  man 236 

242.  Human  skull  showing  enharmosis;  side  view.      X  3 237 

243.  The  same;  front  view 237 

244.  Human  skull  showing  prosharmosis ;  side  view.      X  |         238 

245.  The  same;  front  view 238 

246.  Human  skull  showing  di-enharmosis ;  side  view.     X  I 239 

247.  The  same;  front  view 239 

248.  Human  skull  showing  epharmosis.      X  f       .      .      , 240 

249.  The  fronto-nasal  area 243 

250.  The  naso-labial  area 243 

251.  The  temporal  area : 244 

252.  The  maxillary  area 244 

253.  The  mandibular  area 245 

254.  The  mental  area 245 

255.  The  hyoid  area 246 

256.  The  superior  laryngeal  area 246 

257.  Surface  markings  of  the  lymphatic  system 248 

258.  The  sockets  of  the  teeth  of  man.     X  to 253 

259.  The  sockets  of  the  teeth  of  an  orang-outang.      X  i 253 

260.  The  sockets  of  the  teeth  of  a  hysena.     X  i 254 

261.  The  sockets  of  the  teeth  of  a  Polar  bear.      X  -| 254 

262.  The  sockets  of  the  teeth  of  a  lion.     X  i 255 

263.  Radiograph  of  the  normal  sockets  of  the  teeth  of  a  man,  aged  forty  years 256 

264.  The  same,  of  a  woman,  aged  twenty  years 256 

265.  The  same 256 

266.  The  same,  of  a  man,  aged  nineteen  years 256 

267.  The  same 256 

268.  The  same 256 

269.  The  same 256 

270.  The  same 256 

271.  The  gingival  trough  (Human)  affected  by  "pyorrhoea  alveolaris."      X  Y 258 

272.  The  gingival  trough  of  an  alligator.     X  -*/'        259 


LIST  OF  ILLUSTRATIONS  xix 

Fia.  Page 

273.  The  gingival  trough  of  a  cat.      X  -V 260 

274.  The  same.     X  -1"        261 

275.  The  same.     X  H- 262 

276.  Diagram  of  the  development  of  the  face 264 

277.  The  same;  later  stage 265 

278.  The  same;  later  stage 266 

279.  The  skull  of  an  adult.      X  i 269 

280.  The  skull  of  an  aged  man.      X  f         270 

281.  The  same;  side  view.     X  f 271 

282.  Diagram  of  the  centres  of  ossification  of  the  mandible 272 

283.  Diagram  of  Meckel's  cartilage 276 

284.  The  deciduous  teeth  of  a  child.      X  " 279 

285.  Skull  of  a  child  at  birth.     X  i 279 

286.  The  same,  at  a  later  period.     X  y 279 

287.  The  same.      X  ?- 280 

288.  The  same.     X  ?- 280 

289.  The  same.     X  f 281 

290.  The  same.      X  f 282 

291.  The  same.      X  i'it 282 

292.  Diagram  showing  the  iter  denlis 283 

293.  The  teeth  in  acromegaly 289 

294.  Face  of  an  adult  affected  with  acromegaly 289 

295.  The  same;  side  view 289 

296.  Radiograph  showing  incomplete  eruption  of  the  molars 290 

297.  Diagram  of  a  reflex  act 306 

298.  The  same 306 

299.  Skull  of  a  fruit-eating  bat.      X  y'li 315 

300.  Skull  of  a  hare.     XI 319 

301.  Jaws  of  a  lion.      X  J 321 

302.  Skull  of  a  lion.      X  i 322 

303.  Jaws  of  a  civet.      X  * 323 

304.  Jaws  of  a  long-muzzled  dog.     X  i 323 

305.  Jaws  of  a  sea  otter.     X  |        324 

306.  Skull  of  a  brown  bear.     X  3 325 

307.  Skull  of  an  eared  seal.      X  5 326 

308.  Skull  of  a  dugong.     X  i 330 

309.  Skull  of  a  hyrax.     X  * 334 

310.  Jaws  of  a  horse.     X  § 334 

311.  Skull  of  a  tapir.     X  2 335 

312.  Skull  of  a  rhinoceros.     X  t'o 336 

313.  IVIolars  of  a  tapir,  rhinoceros,  and  a  horse 337 

314.  Skull  of  a  wild  boar.      X  3 33S 

315.  Jaws  of  a  wild  boar.      X  i 339 

316.  Skull  of  a  chevrotain.     X  I 341 

317.  Skull  of  a  water  deer.      X  § 341 

318.  Skull  of  a  camel.     X  i 342 

319.  Skull  of  a  two-toed  sloth.     X  ■, 345 

320.  Jaws  of  a  kangaroo.      X  /'j 348 

321.  Skull  of  a  koala.      X   i"o 349 


XX  LIST  OF  ILLUSTRATIONS 

Fig.  Page 

322.  Skull  of  a  dingo.      X  i 350 

323.  Skiill  of  an  opossum.      X  * 351 

324.  Skull  of  a  bandicoot.      X  | 351 

325.  Jaws  of  a  duck-billed  platypus.      X  f 352 

326.  Skull  of  an  echidna.      X  * 353 

327.  Models  showing  hereditary  absence  of  the  crowns  of  the  teeth.      X  tff 358 

328.  The  same.     X  * 358 

329.  The  same.     X  t5 359 

330.  The  same.     X  ij 359 

331.  The  same.      X  -/„ 360 

332.  The  same 360 

333.  A  non-meduUated  nerve  fibre  in  the  dental  pulp  of  man.      X  ^^ 362 

334.  The  same.     X  -f  °        363 


DENTAL  ANATOMY  AND  PHYSIOLOGY 


CHAPTER  I 


THE  VALUE  OF  THE  STUDY  OF  DENTAL  ANx^TOMY 

Introduction. — Dental  Anatomy  the  Alphabet  of  Dental  Surgery. — The  Utility  of  a  Knowledge 
of  its  Principles. — The  Value  of  the  Stvtdy  of  Comparative  Dental  Anatomy. — Problems 
associated  with  the  Subject,  and  the  Need  for  their  Examination  from  Various  Points  of 
View. — Scheme  of  Succeeding  Chapters,  culminating  in  Human  Dental  Anatomy  Proper. — 
Study  completed  by  brief  Accounts  of  Dentitions  of  the  Order  Mammalia. 

INTRODUCTORY 

On  approaching  the  systematic  study  of  Dental  Anatomy  and 
Physiology  the  work  of  the  student  who  is  about  to  commence  his 
professional  education  is  beset  by  many  difficulties.  He  has,  in  present 
circumstances,  but  little  leisure  to  devote  to  it.  The  pressure  and 
stress  of  other  parts  of  the  curriculum,  more  invaluable  to  his  mind, 
crowd  out  of  his  daily  routine  of  reading,  all  but  a  mere  glance  at 
this  fundamental  basis  of  his  dental  knowledge,  all  but  a  mere  trace 
of  an  acquaintance  with  the  Alphabet  which  constitutes  the  beginning 
of  his  erudition.  The  subject  is  relegated  to  an  inferior  position  in 
his  category  of  studies,  and  it  is  only  when  he  is  nearing  his  final  tests 
for  examination,  that  he  hurriedly  attempts  to  assimilate  the  mere 
outlines  of  a  fascinating  and  really  important  branch  of  natural  science. 
Much  less  does  he  familiarize  himself  with  it. 

In  a  measure  this  is  as  it  should  be.  During  novitiate  days  he 
ought  to  absorb  most  assiduously  those  methods  of  operation  and 
technique  which  will  be  of  most  help  to  him  in  future  practice.  The 
making  of  a  practical  man  is  of  the  first  importance,  but  the  making 
of  a  cultured,  refined  man,  with  an  enlarged  mental  horizon,  is  equally 
important;  and,  of  course,  more  time  must  be  given  to  the  pursuit  of 
practical  matters  than  is  necessary  for  a  complete  grip  of  the  science 


IS  THE   VALUE  OF   THE  STUDY  OF  DENTAL  ANATOMY 

of  Dental  Anatomy.  A  profound  knowledge  of  it  does  not,  per  se, 
enable  a  dental  surgeon  to  prepare  and  fill  a  carious  cavity  in  a  tooth 
in  the  most  efficient  manner  possible.  This  is  more  or  less  a  mechanical 
operation,  and  is  performed  by  a  rule-of-thumb  method,  a  result  of  good 
training  and  extensive  experience.  But  it  does,  undeniably,  assist  him 
to  carry  out  his  intentions  with  regard  to  the  preparation  of  such  a 
cavity,  and  to  the  saving  of  the  tooth  intelligently,  and  much  better 
than  if  he  was  not  conversant  with  the  gross  and  minute  anatomy  of 
the  tissues.  He  must  know  something — yea,  everything  he  possibly  can 
— of  the  structure  of  the  vital  organs  with  which  he  has  to  deal.  For 
the  dental  armament  of  Man  is  part  and  parcel  of  himself.  Teeth  are 
in  their  own  unique  way — and  he  is  apt  to  forget  it — as  much  a  portion 
of  the  anatomy  of  Man  as  are  his  two  eyes  or  his  two  ears.  And  an 
ophthalmic  or  aural  surgeon  could  certainly  not  be  expected  to  know 
anything  of  the  disease  of  these  organs,  if  he  had  never  attempted  to 
study  their  macroscopical  and  microscopical  characteristics. 

THE    ALPHABET    OF    DENTAL    SURGERY    AND    PATHOLOGY 

A  knowledge  of  Dental  Anatomy,  therefore,  is  of  the  utmost  moment 
to  those  students  who  are  training  for  their  life  work  of  dental  surgery. 
It  is  something  that  retains  the  equilibrium  between  things,  relieving 
and  even  beautifying  the  dull  monotony  of  the  mere  drudgery  of  dental 
mechanics  and  operations.  It  acts  very  frequently  as  a  mental  shower 
bath ;  the  mind  is  refreshed  by  it  as  by  a  series  of  experiments  in  mental 
gymnastics.  But,  more  than  this,  it  is  the  very  A  B  C  of  dentistry. 
It  is  impossible  to  be  able  to  read  without  first  learning  all  the  letters 
of  the  alphabet,  then  correlating  them  into  words,  then  grouping 
them  into  sentences,  then  uniting  them  with  the  products  of  intel- 
lectual action — of  memory  and  of  imagination. 

And  so  it  comes  about  that  in  the  treatment  of  affections  of  the 
teeth,  either  individually  or  collectively,  either  from  a  prophylactic  or  a 
therapeutic  point  of  view,  enlightenment  on  this  subject  is  essential. 
Without  it  an  intelligent  grasp  of  the  problems  of  dental  physiology 
and  pathology  is  an  absurd  and  illusive  phantom  and  as  unattainable 
as  an  ignis  fatuus . 


rilE  ALPHABET  OF  DENTAL  SURGERY  AND  PATHOLOGY  19 

There  is,  in  addition,  a  higher  and  still  more  cogent  reason  for  the 
retention  of  Dental  Anatomy  in  the  synopses  of  our  schools,  and  its 
inclusion  in  the  subjects  of  the  qualifying  examination.  Original 
scientific  work  in  the  future  will  have  to  be  undertaken  by  the  student 
of  today,  and  tomorrow.  If  the  chief  facts  and  theories  connected 
with  the  science  of  Dental  Anatomy  were  not  presented  to  him,  and 
his  attention  directed  thereto,  progress  would  be  retarded,  the  work  of 
research  would  be  impeded,  and  dental  science  would  stagnate,  except 
with  regard  to  mere  empirical  and  mechanical  methods  for  the  purposes 
of  making  money. 

The  main  point  then  would  seem  to  be,  in  connection  with  the 
academical  training,  a  lack  of  time  during  the  student's  fulfilment 
of  his  curriculum  in  which  he  can  devote  himself  to  its  study. 

But  another  serious  difficulty  presents  itself.  In  biology  and  zoology, 
scientists  express  themselves — they  cannot  do  otherwise — by  the  use 
of  certain  terms  to  indicate  what  is  meant,  which  are  at  first  quite 
foreign  to  the  ordinary  conception  of  the  student.  Greek  and  Latin 
derivatives  are  largely  used  for  this  purpose,  and  one  of  the  great 
stumbling  blocks  to  a  student's  reading  of  text-books  on  Odontology 
is  the  use  and  signification  of  biological  and  other  terms,  which  are 
quite  new  to  him.  The  subject  is  not  in  itself  so  very  vast,  but  the 
new  unfamiliar  terms  scattered  throughout  it  are  very  numerous. 

It  is  the  purpose  of  the  teacher  of  Dental  Anatomy  to  lighten  the 
work  of  the  undergraduate,  to  facilitate  his  studies,  to  simplify — as  far 
as  is  consistent  with  one's  principles — the  complexities  and  subtleties 
of  his  reading,  to  introduce  him  to  a  new  and  even  romantic  field  of 
Natural  History,  and  to  induce  in  his  mind  a  permanent  and  enthralling- 
enthusiasm  for  the  very  elements  of  his  early  experiences.  It  is  argued 
by  the  critic — w'ho  is  not  only  captious  but  illiterate  and  unscientific 
in  addition — that  these  premises  are  correct  as  far  as  a  knowledge  of 
the  teeth  of  Man  go.  To  such  an  one  it  may  be  pointed  out,  however, 
that  an  acquaintance  with  the  anatomy  and  physiology  of  the  teeth 
of  the  Vertebrates  generally  becomes  necessary  for  a  proper  under- 
standing of  many  physiological  as  well  as  pathological  problems, 
whether  acquired  or  congenital.  For  much  is  to  be  learnt  regarding 
the    development    and    the    morphological    irregularities    and    defects 


20  THE   VALUE  OF   THE  STUDY  OF  DENTAL  ANATOMY 

and  deformities  of  the  teeth  of  Man  by  observing  and  considering  the 
comparative  side  of  the  question.  Such  a  knowledge  cannot  help  but 
throw  an  interesting  side-light  on  many  anomalous  and  diseased  condi- 
tions  seen  in  the  human  oral  cavity. 


SOME    PROBLEMS 

For  instance:  (i)  The  questions  of  the  value  and  relative  impor- 
tance of  the  first  permanent  molar  with  regard  to  the  saving  or  the 
extraction  of  this  tooth  is,  or  ought  to  be,  governed  by  an  exact  com- 
prehension of  its  early  history  as  shown  in  the  development  of  the 
molars  of  Mammalia  generally;  (2)  a  study  of  that  condition  known 
as  hypoplasia  of  the  enamel  should  be  partially  regulated  by  the 
observations  which  follow  the  experimental  feeding  of  small  mammals, 
such  as  mice  or  guinea-pigs,  or  rabbits,  with  meat,  or  vegetables,  or 
artificial  foods;  (3)  accuracy  of  interpretation  of  the  structure  and 
meaning  of  the  presence  of  secondary  or  adventitious  dentine  in  the 
dental  pulp  is  helped  by  a  histological  survey  of  the  dentines  such  as 
osteo-,  vaso-,  or  plici-,  as  met  with  in  fishes;  and  (4)  finally  (although 
it  were  easy  to  multiply  examples)  the  more  abstruse  and  recondite 
problems  connected  with  the  gradual  loss  of  the  teeth  of  Man — an 
incisor  and  a  third  molar — and  the  pathological  conditions  recognized 
as  superior  protrusion  and  circumdental  diseases,  should  be  associated 
with  a  considerable  knowledge  of  the  genesis,  growth,  and  functions 
of  the  maxillary  bones,  and  nasal  fossae  on  the  one  hand,  and  their 
occurrence  in  the  lower  animals  on  the  other. 

There  is  also  another  point  to  be  remembered  with  regard  to  the 
consideration  of  the  comparative  anatomy  of  the  teeth,  in  the  fact 
that  such  a  study  enlarges  a  young  man's  scientific  train  of  thought, 
and  by  bringing  before  him  facts  and  fancies  connected  with  the 
development  and  growth  and  uses  of  the  dental  apparatus  of  fishes, 
reptiles,  and  mammals,  leads  him  to  the  earnest  contemplation  of  the 
romances  and  histories  of  the  fauna  of  the  world  as  seen  either  from 
an  ecological  or  artificial  standpoint.  The  attentive  consideration  of 
the  lives  and  doings  of  animals  is  surely  a  most  alluring  occupation. 


SOME  PROBLEMS  21 

*• 

The  functions  and  uses  of  the  teeth  are  very  varied  and  very  mani- 
fold. The  competent  observer,  in  reply  to  the  enquiry,  "What  is 
the  value  of  the  teeth?"  would  undoubtedly  explain  that  their  main 
functions  were  concerned  with  the  process  of  mastication.  This  is 
correct  as  far  as  it  goes,  but  it  does  not  go  far  enough.  With  regard 
to  the  teeth  of  Man,  probably  the  highest  -function  as  well  as  the 
most  complex,  because  of  its  dependence  on  the  proper  workings  of 
the  higher  cerebral  centres,  that  they  possess,  is  the  power  of  the  pro- 
duction of  speech;  and  the  proper  performance  of  the  mechanism  of  this 
is  dependent  on  the  more  or  less  efficient  state  of  his  dental  organs. 

The  captious  critic  may  affirm,  on  reading  or  hearing  the  above, 
that  the  ideas  associated  with  them  are  not  essential  to  a  proper  under- 
standing and  execution  of  his  daily  work.  He  is  replete  and  contented 
with  his  provincial  egoistic  empiricism.  By  thinking  thus,  however, 
he  debases  his  position  as  a  dental  surgeon  and  becomes  of  the  nature 
of  a  charlatan.  In  fact,  if  a  knowledge  of  Dental  Anatomy  is  with- 
drawn from  a  man's  mind,  or  he  is  prevented  by  various  means, 
from  obtaining  it,  at  once  a  line  is  drawn  around  him,  and  he  is  cut 
ofif  from  the  company  of  those  whose  knowledge  is  based  on  science, 
and  whose  work  is  carried  out  as  the  logical  outcome  of  such  non- 
empirical  formulae  and  doctrines. 

Let  it  be  granted  that  enquiries  are  seldom  forthcoming  by  a  dis- 
criminating person  on  these  points;  at  all  events  it  will  be  agreed  that 
one  ought  to  know  the  most  rudimentary  physiological  processes 
connected  with  the  teeth  and  mouth. 

Let  the  reader  consider  for  a  moment,  for  instance,  the  problem  of 
the  causes  of  the  eruption  of  the  teeth,  and  let  him  recall  the  various 
theories  which  have  gathered  around  it.^  Of  these,  discussed  at  some 
length  in  Chapter  XIV,  the  older  are,  in  brief,  as  follow: 

(i)  Teeth  erupt  on  account  of  the  elongation  of  their  roots; 

(2)  On  account  of  the  general  interstitial  growth  of  the  alveolar 
bone; 

(3)  On  account  of  the  blood  pressure  in  the  pulp,  and  sub-  and 
circumdental  tissues; 

(4)  On  account  of  the  enamel  being  an  epidermal  structure  or  acting 
as  a  foreign  body; 


22  THE   VALUE  OF  THE  STUDY  OF  DENTAL  ANATOMY 

(5)  On  account  of  the  contraction  of  the  alveolar  plates,  and  deposi- 
tion of  bone  at  the  base  of  the  crypts,  and  so  on. 

The  observer  will  at  once  discover  how  a  very  elementary  subject 
like  this  may  be  wrapped  in  obscurity.  If,  however,  he  surveys  the 
problem  from  the  standpoint  of  the  naturalist,  biologist,  and  zoologist 
he  will  find  his  meditations  illumined  by  considering  the  modus  operandi 
which  obtains  in  the  mouths  of  reptiles,  and  the  lower  mammals,  and 
come  to  the  conclusion,  as  the  writer  has  done,  that,  in  spite  of  the 
ingenuity  of  many  of  the  theories,  there  is  only  one  real  explanation 
which  may  be  given  to  an  enquiring  individual,  i.  e.,  that  eruption 
is  a  normal  physiological  process,  governed  by  the  same  forces  which 
are  acting  on  the  other  parts  of  the  body. 

One  cannot  say  exactly  what  forces  determine  the  growth  of  the 
nails,  that  regulate  the  height  of  the  stature,  that  superintend  the 
length  or  abundance  of  the  hair,  that  cause  the  descent  of  the  testes, 
but  it  may  be  believed  that  they  are  nothing  more  nor  less  than  physio- 
logical processes  of  growth  on  the  part  of  Nature,  which  cannot  be 
reduced  to  purely  mathematical  formulae  or  dogma.  The  phenomena 
of  dental  eruption  are  observed  in  the  case  of  odontomes  in  the  jaws, 
of  teeth  which  make  their  way  occasionally  into  the  nasal  fossae 
(Fig.  i),  through  the  cheek,  or  the  facial  surface  of  the  superior  maxilla, 
or  the  sigmoid  notch  of  the  mandible  (Fig.  2),  and  of  organs  which 
erupt  on  the  free  surface  of  the  low  type  of  bone  found  in  certain 
teratomata  (ovarian  "dermoid"  cysts),  Figs.  3  and  4;  and  conversely,^ 
the  laws  of  eruption  are  occasionally  found  to  have  become  suspended 
or  greatly  modified  when  teeth  remain  buried  in  the  jaws  in  an  incom- 
pleted or  fully  developed  condition  (Figs.  5,  6,  and  47). 

In  this  way,  therefore,  a  subject  such  as  this  just  mentioned  should 
be  viewed  and  discussed,  not  only  from  the  standpoint  of  general 
anatomy  and  physiology,  but  from  the  vantage  ground  of  pathology, 
and  last,  but  not  least  important,  of  zoology. 

In  this  connection  another  matter  of  fundamental  interest  might 
perhaps  be  alluded  to,  to  demonstrate  the  utility  of  Comparative 
Dental  Anatomy  in  clarifying  debatable  points.  Many  years  ago  the 
author-  published  an  article  "On  Dentogeny" — the  growth  and 
method  of  formation  of  mammalian  dentine.     In  his  own  opinion  he 


SOME  PROBLEMS 


23 


A  skull  of  an  adult  in  which  a  tooth  had  erupted  into  the  right  nasal  fossa.      X 
Fig.  2 


A  tooth  erupted  into  the  sigmoid  notch  of  the  mandible.      X  yjj. 


24 


THE   VALVE  OF   THE  STUDY  OF  DENTAL  ANATOMY 


then  held,  and  still  holds  more  securely  than  ever,  the  belief  that 
certain  cells  of  the  dental  pulp,  viz.,  the  odontoblasts,  do  not  form 
dentine  matrix,  but  are  chiefly,  if  not  wholly,  concerned  in  acting  as 
trophic  agents  to  the  dentine,  and  probably  as  sensation  carriers  or 
transmitters  to  the  pulp  (see  Chapter  XV). 


Fig.  3 


Three  premolariform  "teeth"  in  an  ovarian 
teratoma.  Side  view.  X  H-  The  original  in 
the  possession  of  Mr.  Aslett  Baldwin. 


Fig.  4 


Tliree  premolariform  "teeth"  in  an  ovarian 
teratoma.  Viewed  from  above.  X  jff-  The 
original  in  the  possession  of  IVIr.  Aslett 
Baldwin. 


This  statement  or  theory  was  not  seriously  challenged,  and  in  some 
quarters  is,  today,  accepted  as  the  probable  truth,  the  building  up 
of  the  matrix  being  ascribed  to  small,  round  cells  on  the  surface  and 
in  the  substance  of  the  pulp  itself.     The  main  argument  advanced 

Fig.  5  Fig.  6 


Radiograph  of  a  horizontally  placed, 
unerupted,  maxillary  canine. 


Radiograph  of  a  similarly  placed 
maxillary  canine. 


against  the  theory  was  that  of  Tomes,  who  wrote  ("A  Manual  of 
Dental  Anatomy,"  p.  173,  1889):  "Comparative  anatomy  furnishes 
evidence  against  the  acceptance  of  such  a  view,  as  many  vasodentines 
which  contain  no  tube  system,  and  so  no  dentinal  fibrils,  are  yet  formed 


SCHEME  OF  SUCCEEDING  CHAPTERS  25 

apparently  by  the  agency  of  a  layer  of  cells,  corresponding  in  most 
features  with  the  odontoblasts  of  other  creatures." 

Thus  sections  of  the  dental  pulp  of  Hake  {Merliicius  vulgaris), 
when  examined  microscopically  in  situ,  under  low  powers,  show  at 
the  periphery,  numerous  long  bodies  which  cursorily  appear  to  be 
homologous  with  mammalian  odontoblasts.  On  higher  magnifica- 
tion it  is  seen  that  they  are  non-nuclear,  and  that  they  are  merely 
bundles  of  connective-tissue  fibres  arranged  like  the  constituents 
of  the  niembrana  eboris,  and  are  not  structurally  or  functionally  com- 
parable to  these  cells. 

Four  years  later,  therefore,  Tomes  modified  this  statement,  and 
remarked:  "We  have  always  been  accustomed  to  say  that  they  (the 
odontoblasts)  formed  the  whole  of  the  dentine;  now  we  know  that 
they  do  not"  {Journal  of  the  British  Dental  Association,  vol.  xiv, 
p.  474). 

It  is  interesting  to  add  that  Walkhoff,^  too,  considers  that  the  pro- 
cesses of  the  odontoblasts  serve  essentially  for  the  nutrition  of  the 
dentine.  And  Korff^  and  Studnicka,''  still  more  recently,  indepen- 
dently endorse  these  views.  Thus  MM.  Dieulafe  and  Herpin^  write: 
"Les  odontoblastes  ne  secreteraient  que  les  gaines  de  Neumann." 

So  it  can  be  understood  that,  at  first,  comparative  anatomy 
destroyed  this  theory,  but  on  further  examination,  built  it  up  again 
and  established  it  on  still  surer  foundations. 


SCHEME  OF  SUCCEEDING  CHAPTERS 

The  course  of  a  person's  study  in  dental  anatomy  must  be  regulated 
largely  by  local  conditions.  The  subject  is  world-wide.  From  east 
to  west  it  is  taught  in  the  dental  schools  of  civilized  countries.  And 
in  conclusion,  the  author  ventures  to  offer  in  subsequent  pages,  what 
appears  to  him  to  be  the  best  means  to  be  adopted  by  which  an  intelli- 
gent and  logically  sequential,  if  necessarily  brief,  survey  of  the  subject 
can  be  conveniently  adapted  to  the  needs  of  the  already  overcrowded 
dental  curriculum. 

In  unfolding  a  new  design  to  an  artist,  in  opening  up  an  undiscovered 


26  THE   VALUE  OF   THE  STUDY  OF  DENTAL  ANATOMY 

territory  to  a  would-be  explorer,  it  is  wise  to  argue  "from  the  known 
to  the  unknown."  It  is  futile  to  jumble  together  facts  and  state- 
ments, and  allow  the  student  to  stumble  through  the  mass,  so  that, 
peradventure,  a  few  salient  features  may  remain  in  his  memory. 

The  functions  of  the  teeth  form  an  excellent  introduction  to  the 
subject.  Universal  is  the  knowledge  of  the  uses  of  the  teeth  for  the 
purposes  of  speech  and  mastication,  but  it  is  not  so  generally  known 
that  the  latter  includes  comminution  and  trituration  of  food,  that 
some  herbivorous  animals,  for  instance,  browse  on  leaves,  while  some 
graze,  as  the  giraffe  and  sheep  respectively.  One  would  have  thought 
that  all  elephants  would  have  possessed  similar  teeth,  but  the  coronal 
patterns  of  the  Indian  and  African  species  vary  greatly,  on  account 
of  the  widely  different  foods  which  they  have  to  comminute.  (See 
Fig.  6i.) 

By  pointing  out  these  things,  a  student's  imagination  is  at  once 
fired,  and  he  begins  to  take  an  interest  in  his  newly  found  knowledge. 
The  highest  point  of  study  should  be,  naturally,  the  naked-eye  anatomy, 
the  histology,  and  the  physiology  of  the  teeth  of  Man.  And  in  order 
to  reach  this  point,  the  discussion  on  the  functions  of  the  teeth  is 
suitably  and  profitably  followed  by  the  presentation  to  the  student  of 
the  number  of  the  teeth  of  fishes,  reptiles,  and  mammals,  the  shapes 
of  the  teeth  crowns,  the  reason  why  they  should  assume  these  various 
shapes,  with  illustrations  on  the  "adaptive  modification"  of  organs, 
natural  and  sexual  selection,  and  a  disquisition  on  evolution  as  set 
forth  by  Darwin  and  others.  The  way  is  then  paved  for  the  proper 
consideration  of,  perhaps,  one  of  the  most  difficult  of  all  dental  anatomi- 
cal studies — the  homologies  of  the  teeth  and  its  bearing  on  the  human 
dentitions.  Then  comes  the  purely  Dental  Anatomy  of  the  teeth  of 
the  Primates,  including  Man,  succeeded  by  the  minute  anatomy  of  the 
tissues,  the  histogenesis  of  the  teeth,  and  modes  of  formation  of  the 
hard  and  soft  tissues,  with  the  growth  of  the  jaws  and  the  functions 
of  the  various  parts.  The  climax  to  the  study  is  reached  by  studying 
the  changes  that  the  jaws  undergo  in  infancy,  adult  life,  and  old  age. 

The  work  is  completed  by  brief  glances  at  the  dentitions  of  the 
other  orders  and  families  of  mammals,  beginning  with  the  Cheiroptera, 
and  finishing  with  the  Monotremata;  is  supplemented  and  greatly  helped 


SCHEME  OF  SUCCEEDING  CHAPTERS  27 

by  the  use  of  explanatory  illustrations,  is  raised  to  a  high  level  by 
the  association  of  the  ideas  and  theories,  and  facts  set  forth  with  the 
working  of  the  daily  experience  of  men,  in  dental  surgery  and  path- 
ology; and  should  remain  permanently  fixed  in  the  heart  of  the  student 
as  a  pleasant  and  profitable  memory  and  source  of  great  delight. 

References 

1.  Dieulafe  et  Herpin.    "L'Anatomie  de  la  Bouche  et  des  Dents,"  Traite  de  Stomatologie,  Fasc.  I, 
1909. 

2.  Hopewell-Smith.     "  On  Dentogeny,  "  TJie  Dental  Record,  1889. 

3.  Korff.     "Die  Analogic  in  der  Entwickelung  der  Knochen  und  Zahnbeinsubstanz, "  Archiv. 
fur  micros.  Anat.,  1907. 

4.  Studnicka.    "Die  radialen  Fibrillensystem  bei  der  Dentinbildung  und  im  Entwickelten  Dentin 
der  Saugethiere,"  Aiiat.  Anzeiger,  t.  xxx,  1907. 

5.  Tomes,  Clias.  S.    "A  Manual  of  Dental  Anatomy,  Human  and  Comparative,"  1904. 

6.  Walkhoff.     "Die  Normale  Histologic  Menschlichen  Zahne, "  1901. 


CHAPTER    II 
THE   TEETH   AND   THEIR   FUNCTIONS 

Introduction. — Definitions. — Kinds  of  Teeth. — General  Major  Functions. — Foods  of  Fishes, 
Reptiles,  and  Mammals. — The  Food  of  Man  in  Europe,  Asia,  Africa,  America,  and  Melanesia. 
— As  Factors  in  Facial  Development. — The  Specific  Major  Functions  of  Speech,  of  Ornamen- 
tation, of  Emotional  Expression. — The  Minor  Functions  of  Prehension,  of  Sexual  Warfare, 
of  Transport  and  Locomotion,  of  Offence,  of  the  Toilet,  of  Chiselling,  of  Protection  from 
Injury,  of  Sifting  Food,  of  the  Production  of  Sounds,  and  of  Attack. — Functionless  Teeth. — 
Dental  Substitutes. — AppUcation  of  Nature  to  the  Requirements  of  Art. 

INTRODUCTION 

Various  attempts  have  been  made  to  classify  those  organized  bodies 
endowed  with  hfe  and  voluntary  movements  which  are  known  as 
animals,  from  the  time  of  Aristotle  (b.  c.  350),  who  divided  them  into 
red-blooded  and  white-blooded  or  ex-sanguineous  creatures,  to  the 
present  day.  The  names  of  Linnaeus,  John  Hunter,  Lamarck,  Cuvier, 
Grant,  Lydekker,  and  RayLankester  are  prominent  among  the  savants 
who  have  made  Natural  History  a  special  study.  It  is  thus  evident 
that  several  classifications  exist.  None  are  strictly  accurate:  all  .are 
open  to  objection.  For  present  purposes,  however,  it  may  be  said 
that  the  Animal    Kingdom  may  provisionally  be  divided  into: 

Sub-kingdom         I.      Vertebrata — Vertebrates. 
Class         I.     Mammalia — Mammals. 

Sub-class    I.     Prototheria,  i.  e.,    first   or   primitive 
mammals. 

Sub-class  II.     Eutheria,  i.e.,  ordinary  mammals. 
Class       II.     Aves — Birds. 
Class     III.     Reptilia — Reptiles. 
Class      IV.     Amphibia — Amphibians. 
Class        V.     Pisces — Fishes. 

Class      VI.      Cydostoma — Lampreys  and  hag-fishes. 
Class    VII.     Protochorda. 
Class  VIII.     Hemichorda. 


Sub-kingdom 

II. 

Sub-kingdom 

III. 

Sub-kingdom 

IV. 

Sub-kingdom 

V. 

Sub-kingdom 

VI. 

Sub-kingdom 

VII. 

Sub-kingdom 

VIII. 

Sub-kingdom 

IX. 

THE   TEETH  IN  GENERAL  29 

Arthropoda — Crustaceans  and  insects. 

Mollusca — Oysters,  snails,  and  whelks. 

Brachiopoda — Lampshells. 

Echinoderma — Starfish . 

Bryozoa  or  Polyzoa — Moss  animals. 

Vermes — Worms. 

Ccelentera — Sponges,  corals,  etc. 

Protozoa — Animalculae. 

The  following  pages  are  concerned  with  the  Dental  Anatomy 
and  Physiology  of  the  Vertebrata,  particularly  of  Class  I,  and  less 
importantly  of  Classes  III,  V,  and  VI. 


THE    TEETH    IN    GENERAL 

Definitions. — It  is  remarkable,  but  nevertheless  true,  that  in  spite 
of  much  anatomical  and  pathological  knowledge  of  the  teeth,  it  is 
impossible  to  give  an  accurate  definition  of  them.  John  Hunter, 
the  Father  of  Odontological  Science,  whose  extraordinary  and  unique 
work  "The  Natural  History  of  the  Human  Teeth"  was  published  in 
1771,  did  not  define  them.  Owen"  described  them,  in  his  "Odontog- 
raphy" (1840),  as  "Firm  substances  attached  to  the  parietes  of  the 
beginning  of  the  alimentary  canal,  adapted  for  seizing,  lacerating, 
dividing,  and  triturating  food,  the  chief  agents  in  the  mechanical 
part  of  the  digestive  function."  This  definition,  appropriate  at  the 
time  of  Owen's  writings  (1840-70),  fails  today,  as  will  be  seen  presently. 
A  shorter  description  might  read  as  follows:  "Teeth  are  the  hard 
bodies  in  the  mbuth,  attached  to  the  skeleton,  but  not  forming  part 
of  it,  developed  from  the  dermis,  or  true  skin;  their  functions  primarily 
being  the  comminution  of  the  food." 

The  definitions  just  given  describe  sufficiently  succinctly  the  teeth 
as  the  student  knows  them;  but,  in  the  realms  of  comparative  embry- 
ology and  in  general  pathology,  structures  are  found  which  correspond 
morphologically  so  closely  to  them  that  one  is  justified  in  calling  them 
dental  organs.  Bland-Sutton-  has  noticed  that  sheep  are  particularly 
liable  to  an  anomalous  condition  of  the  skin  in   the  neighbourhood 


30 


THE   TEETH  AND   THEIR  FUNCTIONS 


of  the  ear  (Fig.  7).  Occasionally  a  fistulous  opening  is  found  near 
the  base  of  the  auricle,  the  surface  of  M'^hich  is  surmounted  by  a  tooth, 
invariably  of  an  incisor-like  pattern.  This  circular  orifice  he  believes 
to  be  an  accessory  mouth  which  is  usually  single,  but  at  times  it  may 
be  associated  with  a  small  mandible  and  tongue.  He  writes:  "The 
cervical  teeth  and  the  associated  structures  are  remnants  of  an  attached 
or  parasitic  creature,  and  the  cutaneous  opening  represents  its  mouth." 
He  has  also  found  tooth-like  bodies  attached  to  the  temporal  bones 
of  horses,  and  recorded  40  cases  in  which  they  were  present. 


Outline  drawing  of  the  head  of  a  hornless  sheep, 
showing  (at  X)  an  incisiform  tooth  near  the  base 
of  the  auricle.     (After  Bland-Sutton.) 


A  caniniform  tooth  developed  in  and 
attached  to  the  wall  of  an  ovarian  terato- 
matous  C3'St.      X  \. 


There  are  two  theories  as  to  the  cause  of  the  presence  of  the  teeth 
in  this  situation.  Bland-Sutton  considers  that  they  are  probably  due 
to  parasitism,  as  they  are  usually  unilateral;  but  other  writers  believe 
them  to  be  due  to  a  developmental  error,  connected  with  the  first 
branchial  cleft.  In  this  case  involution  of  the  teeth-bearing  part  of 
the  palato-pterygoid  division  of  the  first  branchial  arch  would  have 
occurred. 

Interesting  as  these  are  from  a  comparative  point  of  view,  perhaps 
even  more  instructive  still  are  the  dental  bodies  found  in  certain 
embryomatous  cysts,  the  so-called  ovarian  "dermoid"  cysts.     These 


THE   TEETH  IN  GENERAL  31 

morphologically  correspond  to  premolars  and,  more  rarely,  incisors 
or  canines,  being  usually  attached  to  a  degenerated  bone  which  is 
homologous  with  the  alveolar  process  of  the  jaws,  or  occasionally 
to  the  soft  tissues  of  the  wall  of  the  teratomatous  cyst.^ 

Bland-Sutton  gives  an  illustration  in  his  "Tumors,  Innocent  and 
Malignant,"  of  a  "dermoid"  cyst  containing  hair  and  "teeth,"  which 
was  situated  behind  the  rectum;  also  another  of  a  dermoid  found  in 
the  left  naso-facial  sulcus  which  possessed  a  "tooth."  Other  anomalous 
positions  of  "teeth,"  further,  observed  by  this  author,  occurred  in  a 
congenital  embryoma  of  the  testis  of  a  Chinese  boy,  which  can  be  seen 
in  the  Museum  of  the  Royal  College  of  Surgeons  of  England,  where 
it  is  shown  presenting  "the  usual  sebaceous  matter,  loose  hair,  and 
an  embryonic  rudiment  consisting  of  bone,  hyaline  cartilage,  and  a 
multi-cuspidate  tooth;"  and  also  in  the  undescended  testes  of  horses, 
which,  "like  typical  ovarian  dermoids,  contain  an  ill-developed 
embryonic  rudiment  contained  in  a  cyst,  covered  with  pilose  skin  and 
stuffed  with  loose  hair,  grease,  and  occasionally  teeth  resembling  equine 
incisors."  These  latter  occurring  in  males  are  probably  produced  by 
hermaphroditic  impregnation.'-^ 

The  upper  tusks  of  the  male  Malay  wild  boar  (see  Fig.  28)  are 
placed  entirely  extra-orally. 

Hence  it  is  obvious  that  the  definitions  just  given  do  not  scientifically 
represent  the  term  "teeth." 

Kinds  of  Teeth. — Among  the  Vertebrates  there  are  two  kinds  of 
Teeth:     (i)  Corneous;  and  (2)  Calcified. 

Comparative  Dental  Anatomy  has  little  to  do  with  the  former, 
though  in  the  Mammalian  Order  of  the  Monotremes,  the  Ornitho- 
rhyiichus  and  th'e  Echidna  possess  horny  plates,  which  perform  the 
functions  of  the  teeth.  Amongst  the  Cydostomata,*  the  mouth  of  the 
lamprey  is  beset  with  corneous  triangular  or  multicuspidate  bodies, 
developed,  no  doubt,  from  an  epithelial  layer  of  cells,  which  go  no 
further  than  forming  a  tough  keratinous  substance  (Fig.  9).  In  the 
myxine  there  is  one  corneous  tooth  on  the  palate,  superposed  over  a 

*  The  Cydostoma  (Ki;/c^(of  =  round,  cTu/j.a=  mouth)  comprise  Class  VI  of  the  Vertebrata,  and  thus 
form  a  class  distinct  from,  and  more  lowly  organized  than  the  fishes,  inasmuch  as  they  possess 
no  jaws,  have  a  single — not  a  double — nasal  aperture,  and  a  rasping  tongue. 


32 


THE  TEETH  AND  THEIR  FUNCTIONS 


horn-forming   epithelium,    which   has,   on   its  under   surface,    a   small 
amount  of  enamel  and  dentine.-^ 

It  is  unnecessary  to  point  out  that  the  birds  of 

fj.    .,  today  do  not  possess  a  dental  armament.     It  is 

interesting,  however,  to  note  that  the  penguin's 

tongue  is  beset  with  long  corneous  papillae  whose 

function  is  identical  with  that  of  the  lingual  teeth 

of  many  fishes.     This  is  well  described  in  Brooke 

Nicholls'^  "The  Teeth  of  the  Australian  Animals." 

Some  Mollusca,  like  the  whelk  and  snail,  have 

radidce  in  their  mouths   which  are  covered   with 

minute  teeth.     There  may   be  as  many  as  three 

hundred    in    some    species.      Viewed    under    the 

microscope,    either  by    transmitted  light  or  with 

Head  and  mouth  of  a  sea     the  help  of  the  polariscopc,  they  make  beautiful 

lamprey.     X  j.  objects  (Figs.  lo  and  II). 


V 

Palate  of  a  marine  gastcrupod  {HaliDlis),  showing  an  axial  part  covered  with  a  few,  large,  straight- 
edged  teeth,  an  intermediate  part  with  large  serrated  teeth,  and  an  external  part  eovered  with  many 
rows  of  sharp,  pointed  teeth.     X  -p. 


THE  FUNCTIONS  OF   THE   TEETH 


33 


In  order  to  grasp  the  subject  of  Dental  Anatomy,  which  includes 
studies  in  biology,  zoology,  ethnology,  and  anthropology,  as  well 
as  general  anatomy  and  palaeontology,  it  is  best  to  argue  from  the 
known  to  the  unknown.     The  reader 

knows  something  about  the  functions  Fig.  n 

of  his  own  teeth.  This,  therefore, 
seems  to  be  an  excellent  starting 
point  for  an  excursion  into  this  little- 
explored  territory. 

THE    FUNCTIONS    OF    THE 
TEETH 

The  functions  of  the  teeth  con- 
sidered collectively  may  be  divided 
into  two  classes,  Major  and  Minor, 
and  the  former  further  subdivided 
into  General  and  Specific. 

General  Functions 

Of  the  former,  the  comminution 
of  food  is  universal.  It  will  be 
noticed  that  the  word  "comminu- 
tion" is  used  instead  of  the  word 
"mastication,"  for  it  indicates  more 
than  is  implied  in  mere  mastication 
— it  denotes  thfe  preparation  of  the 
food  for  assimilation  by  the  diges- 
tive tract,  by  its  reduction  to  small 
particles  before  its  passage  into  the 
oesophagus. 

The  lives  of  fishes,  reptiles,  and  mammals  depend  upon  the  proper 
assimilation  of  their  food.  Its  preparation  depends  upon  the  func- 
tions of  their  teeth.  All  mature  living  creatures  can  feed  themselves, 
and  all   possess  organs  which  have  masticatory  powers,   whose  uses 

3 


Radula  (tongue  or  lingual  ribbon)  of  a 
marine  mollusc,  to  show  the  numerous 
sharp,  pointed  teeth.  At  A  seven  teeth 
have  become  detached.      X  ~f-- 


34  THE   TEETH  AND   THEIR  FUNCTIONS 

are  very  diversified  with  regard  to  the  various  kinds  of  food  which 
they  comminute.  The  Amazonian  ant,  Polyergus,  is,  with  one  excep- 
tion, the  only  instance  of  a  Uving  creature  which  has  lost  its  natural 
instinct  oi  feeding  itself}^ 

The  Foods  of  the  Vertebrates. — Fishes. — The  food  of  Fishes  is 
extremely  varied.  It  consists  of  aquatic  plants  and  living  creatures. 
Thus  some  members  of  the  carp  order  {Physostomi),  subsist  on  marine 
vegetable  substances  which  require  efficient  mastication,  a  work 
accomplished   by   the  pharyngeal  bones;  some   are   flesh   feeders,   and 

Fig.  12 


Jaws  of  wolf-fish  (Anarrhjcas  lupus).     Side  view 


others  live  on  the  protozoa  and  small  animals  found  in  abundance 
in  shallow  pools.  The  herring  feeds  on  small  crustaceans  like  water 
fleas,  60,000  of  which,  according  to  Schmeil,^"  may  constitute  a  meal; 
and  the  lamprey  scrapes  off  the  skins  of  fishes  and  then  sucks  up  the 
blood  and  other  body  juices  and  soft  parts.  The  shells  of  molluscs 
are  largely  eaten  by  such  creatures  as  the  plaice,  the  wolf-fish  (Anar- 
rhichas  lupus)  (Fig.  12),  etc.,  while  small  fishes,  insect  larvae,  and 
marine  worms  fall  victims  to  the  sturgeon.  The  carrion  of  the  sea 
and  the  kitchen  refuse  of  ships  provide  food  for  the  shark. 


THE  FOOD  OF  MAN  35 

Reptiles. — Among  the  Reptiles,  lizards  eat  butterflies,  beetles, 
crickets,  insect  larvae,  flies,  spiders,  earthworms,  etc.  Snakes  devour 
amphibians  and  their  larvae  and  fish.  Vipers  eat  mice;  crocodiles 
principally  fish;  and  tortoises  fish,   amphibians,  worms,   and  insects. 

Mammals. — The  food  of  Mammals  is  of  a  most  mixed  and  extensive 
character.  Thus,  there  are  fruit  eaters,  as  the  apes,  who  also  utilize 
for  the  same  purpose  young  leaves  and  buds;  the  carnivorous  animals, 
such  as  cats,  etc.;  the  vegetable  feeders,  such  as  the  deer;  the  fish 
eaters,  such  as  the  seals;  and  the  omnivorous  animals,  such  as  Man, 
the  pig,  the  wild  boar,  bear,  etc.  Bats  are  fruit  and  insect  feeders; 
rodents — gnawing  animals — subsist  on  vegetable  substances,  includ- 
ing those  found  in  forests,  viz.,  nuts,  beechnuts,  acorns,  etc.  The 
elephant  is  herbivorous — but  the  African  and  the  Indian  varieties 
consume  different  kinds  of  vegetable  matter.  The  whale  is  carniv- 
orous, e.  g.,  the  Greenland  whale  by  means  of  its  whalebone  plates 
living  on  myriads  of  small  but  highly  nutritious  crustaceans  and 
pteropods.  Among  the  animals  inhabiting  the  Australian  continent 
the  kangaroo  eats  grass,  the  duck-billed  platypus  molluscs,  water 
plants,  worms,  etc. 

The  Food  of  Man. — As  the  comminution  of  food  constitutes  the 
most  universal  function  of  the  teeth,  it  will  be  profitable  to  take  a 
momentary  glance  at  the  constitution  of  the  dietaries  of  mankind, 
which  probably  play  such  an  important  part  in  the  incidence  of  dental 
caries.  Although,  generally  speaking,  there  is  no  deviation  from  the 
standard  patterns  and  types  of  human  teeth,  the  races  of  the  world, 
living  in  varying  environments,  eat  different  kinds  of  food. 

A  brief  summary  of  these  national  diets  may  be  given. 

European.  —  (i)  Belgium. — The  principal  articles  of  food  are 
great  quantities  of  fat,  in  the  form  of  butter,  lard,  and 
"margarine." 

(2)  Denmark. — The  staple  diet  is  similar  to  that  of  the  British 
Isles,  but  it  comprises  less  meat  and  vegetables,  more  potatoes, 
rice,  and  other  starch-containing  bodies. 

(3)  Greece. — The  poorest  of  the  people  mainly  eat  vegetables 
in  summer  and  legumes  in  winter,  all  mixed  with  olive  oil; 
the  richer  classes,  meat  cooked  in  butter.     Fish  is  consumed 


36  THE  TEETH  AND  THEIR  FUNCTIONS 

on  the  sea  border.    Bread  and  butter  are  practically  never  eaten, 
and  pork  but  little. 

(4)  Iceland. — Fatty  foods  (butter  and  suet)  are  universal, 
and,  on  account  of  the  intense  cold,  more  indulged  in  than 
in  any  other  country.  Potatoes  are  used  extremely  largely; 
of  other  vegetables  practically  none.  Beef,  mutton,  fish,  black 
bread,  and  bread-stuffs  generally  are  staple  articles  of  diet. 
The  use  of  coffee  is  general,  but  that  of  tea  is  rare,  while  that 
of  intoxicating  drinks  is  less  frequent  than  elsewhere. 

(5)  Italy. — Meat  and  fat  are  very  little  eaten,  except  the 
latter  in  the  form  of  oil.  Maize,  known  as  polenta,  constitutes 
the  main  feature  of  the  Italian  regimen. 

(6)  The  Netherlands. — Bread  and  potatoes  are  partaken  of 
largely,  as  also  are  great  varieties  of  vegetables  and  albumens 
and  fats  amongst  the  higher  classes. 

(7)  Roumania. — The  peasants,  according  to  Lucas  Champion- 
niere,  eat  vegetables;  town  dwellers  an  animal  diet. 

(8)  Spain. — The  poor  man's  chief  sustenance  consists  of  a  thin 
decoction  of  innutritions  meat,  rice,  bread,  and -water  boiled  up 
day  after  day  with  occasional  additions,  according  to  Bryden 
Hendinning,  of  "that  which  fortune  may  send  and  of  garbage." 
The  well-to-do  classes  adopt  a  French  cuisine. 

(9)  Sweden. — In  winter,  potatoes  are  the  only  vegetable.  It 
has  been  computed  that  the  amount  of  meat  averages  28  kilo- 
grammes per  head,  milk,  183  litres,  and  butter,  5>^  kilogrammes. 
Rye  is  used  more  generally  than  wheat.  Smoked,  salted,  and 
dried  animal  food  is  eaten  as  a  relish  with  butter  and  hard 
bread. 

Asiatic. — (i)  China. — The  poor  have  no  meat.  Rice  is  universally 
consumed,  one  to  three  bowlfuls  being  eaten  at  each  meal,  with 
salted  beans,  fish,  or  turnips  as  relishes.  Occasionally,  fresh 
pork  or  mutton  is  procured.  Sugar  is  found  on  the  tables  of 
the  rich  and  at  feasts,  but  otherwise  is  little  used,  while  edible 
birds'  nests  are  frequently  eaten.  According  to  the  Scientific 
American,  in  the  year  1909,  the  weight  of  the  edible  birds' 
nests    collected    in    the    islands    about   Siam   and   the   Malay 


THE  FOOD  OF  MAN  37 

Archipelago    amounted    to   eighteen    thousand    pounds,    valued 
at  about  £20,000.     The  taking  of  the  nests  is  fully  described. 
It  is  stated  that  the  birds  require  three  months  to  build  the 
first  nests,  which  are  gathered  before  any  eggs  are  laid.    Thirty 
days  are  occupied  in  building  a  second,  which  is  taken  in  a 
similar  way.     The  third  nest  is  left,  but  after  the  young  are 
reared,  it  is  also  taken  and  sold.  .  After  washing  in  cold  water, 
the  nests  are  cooked  for  eight  hours.     Various  views  as  to  the 
exact  nature  of  the  nest  used  in  making  the  famous  Chinese 
delicacy,  bird's-nest  soup,  have  been  held.      According  to  the 
above  article  it  is  now  known  that  they  are  formed  of  a  species 
of  seaweed  gathered  by  the  birds.     Unfortunately  no  authority 
is  given  for  the  statement.     In  Professor  Newton's  article  in 
the'' "Encyclopaedia  Britannica"  it  is  stated  that  they  are  made 
of  a  sort  of  mucus  secreted  by  the  salivary  glands  of  the  birds 
themselves.     The  builders  of   the   nests  are  species  of  swifts 
belonging  to  the  genus  known  to  ornithologists  as  Collocalia. 
In  the  English  swift  the  salivary  glands  are  largely  developed, 
and  the  secretion  is  used  to  glue  together  the  materials  of  the 
nest.     But  in  the  Collocalia  it  forms  "almost  the  whole  sub- 
stance of  the  structure."     "This  view,"  says  Professor  Newton, 
"has  been  needlessly  doubted  in  favour  of  the  popular  belief 
that  they  were  made  of  some  sort  of  seaweed."     This  is  sup- 
ported by  reference  to  analysis  of  the  nest  made  by  Mr.  J.  R. 
Green.     On  the  other  hand,  Landor,  who  observed  the  birds 
in  the    Philippine  Islands,  says  that    they  use    the  gum    from 
certain  "trees  for  their  nests. 

The  Chinese  suffer  from  insufficiency  of  mastication,  with  all 
its  attendant  evils. 

(2)  India.^ln  the  Punjaub  sour  milk  is  an  article  of  diet  with 
the  morning  meal.  The  Jains  are  strict  vegetarians.  Sir  George 
Birdwood  writes:  "The  Hindus  eat  an  inordinate  quantity  of 
sugar,  and  some  of  their  castes  also  of  curry,  and  other  scorch- 
ing savouries,  as  also  of  all  sorts  of  corrosive  pickles,  than 
which  nothing  can  be  more  destructive  of  teeth.  The  true 
causes  of  their  having  fine  teeth  are,  among  others:     (i)  Their 


38  THE   TEETH  AND   THEIR  FUNCTIONS 

habit  of  cleaning  them  with  the  yielding  soft  twigs  of  certain 
sacred  trees;  (2)  and  of  chewing  'betelnut'  {Areca  catechu), 
with  'betel-leaf  {Piper  betel)  (this  habit  originating  in  the 
primitive  typological  rite  of  reddening  or  blackening  the  teeth, 
and  drilling  holes  in,  or  knocking  out  one  or  two  of  them,  on 
the  young  men  and  maidens  of  a  community  becoming  marriage- 
able, and  still  prevailing  among  the  Aborigines  of  the  Indian 
Archipelago),  this  habit,  in  the  case  of  vegetarians,  like  the 
Hindus,  serving  not  only  to  mitigate  the  flatulence  of  their 
diet,  but  strongly  to  consolidate  their  gums;  and  (3)  above 
all  to  the  universal  Oriental  habit,  imperative  among  Hindus, 
of  having  their  children  submitted  before  marriage  to  the 
most  anxious  physical  inspection,  particularly  of  the  teeth 
and  nails  (teeth  being  'doublets'  of  nails,  as  the  upper  and 
lower  jaws  are  of  the  arms  and  legs,  and  the  head  of  the  whole 
trunk).  They  regard  fine  teeth  and  nails  as  the  most  convinc- 
ing credentials  of  a  sound  and  vigorous  constitution,  and  the 
happiest  guarantees  of  male  descendants.  Their  sound  teeth 
are  the  result  of  at  least  3000  years'  practice  of  these  religious 
rites." 

(3)  Persia. — According  to  Dr.  Neligan,  the  Persian  is  a  gross 
feeder,  and  his  diet  is  simple  and  soft.  Fat  is  largely  eaten  by 
all  classes.  The  food  eaten  in  Teheran  is  much  the  same  as 
in  the  provinces,  but  is  not  of  such  good  quality.  The  richer 
natives  (Persians  and  Armenians)  also  consume  European 
dishes,  tinned  meats,  etc.  The  Persian  takes  a  large  quantity 
at  a  sitting  and  bolts  it;  he  has  practically  only  two  meals  in 
the  day,  one  at  midday,  the  other  just  before  bedtime.  Whole- 
meal bread  is  the  staple  article  of  food;  meat  and  rice,  " chillau" 
and  "pillau,"  are  eaten  largely  by  the  richer  classes  only; 
large  quantities  of  fruit  are  partaken  of  in  the  season,  especially 
melons,  grapes,  pomegranates,  and  dates.  The  most  popular 
vegetables  are  lettuce,  cucumber,  and  beetroot;  cheese  made 
from  goats'  milk  is  largely  consumed.  In  the  spring,  Persians 
of  all  classes  drink  large  quantities  of  curdled  milk,  of  butter- 
milk,  and  of  sherbert  made  of  the  juices  of  fruits  with  iced 


THE  FOOD  OF  MAN  39 

water.  Everything  cooked  is  drowned  in  fat  "roghan;"  it  is 
a  form  of  "ghee,"  or  clarified  butter,  made  from  sheep's  and 
goats'  milk,  and  varies  in  quality,  but  that  generally  used  is 
very  offensive  in  smell,  taste,  and  appearance.  The  meat 
eaten  is  almost  entirely  mutton  of  poor  quality.  For  those 
who  cannot  get  meat,  a  broth  made  by  simmering  lumps  of 
meat  and  fat  in  water  for  many  hours  is  used.  Animal  fat  is 
also  indulged  in,  in  large  quantities,  by  the  richer  classes,  in 
the  form  of  "kabobs,"  which  consists  of  alternate  cubes  of  meat 
and  fat  grilled  on  a  skewer  over  a  brazier.  The  Persian  stomach 
delights  in  bitter  and  acid  things;  its  owner  cooks  all  sorts  of 
bitter  plums,  fruits,  and  herbs  with  his  food.  Tea  is  freely 
drunk;  it  is  taken  very  weak;  also  a  native  spirit  called  "arak." 

(4)  Ceylon. — The  Veddas  of  Ceylon  (the  aboriginal  inhabi- 
tants), who  live  amongst  the  forests,  "subsist  chiefly  on  roots, 
fish,  honey,  iguana  lizards,  and  the  products  of  the  chase,  such 
as  the  Wadura  monkey,  the  deer,  and  the  wild  boar.  In  their 
choice  of  food  they  are  omnivorous,  no  carrion  or  even  vermin 
being  too  repulsive  to  suit  their  appetite;  and  grain  and  fruits, 
when  procurable,  are  used.  Being  skilful  archers,  they  bring 
down,  with  their  long  arrows,  such  prey  as  bats,  crows,  owls, 
and  kites,  but  for  some  curious  reason  they  will  not  touch  the 
bear,  the  elephant,  or  the  buffalo.  .  .  .  Their  food  is 
always  cooked.  .  .  .  They  never  wash,  thinking  it  would 
weaken  them,  and  they  never  laugh. "-'- 

(5)  Arabia. — The  peoples  of  Arabia  have,  as  food-stuffs,  wheat, 
maize,  and  barley.  The  date  is  the  staple  article  of  commerce, 
and  their  chief  food.     Coffee  is  largely  drunk. 

African. — (i)  Abyssinia. — Beef  in  a  warm,  raw  condition  at  cer- 
tain periods  of  the  year  is  used.  Mutton,  chicken,  etc.,  and 
leguminous  vegetables  are  mixed  with  red  pepper,  together 
with  various  spices  and  a  large  amount  of  melted  butter,  the 
sole  fatty  constituent  of  the  diet.  The  staple  article  of  food 
is  a  small  grain  cereal  known  as  "teff,"  chiefly  composed  of 
carbohydrates,  with  a  small  admixture  of  proteid  material. 
Hydrocarbons  are  absent. 


40  THE  TEETH  AND  THEIR  FUNCTIONS 

(2)  Bushmen. — The  Bushmen  hve  on  game,  which  they 
kill  by  poisoning.  With  the  exception  of  goat  flesh,  they  eat 
anything  that  is  edible.  When  large  game  is  wanting,  their 
diet  consists  of  locusts,  the  bodies  and  eggs  of  termites  (white 
ants),  wild  beans,  and  roots.  Putrid  meat  is  partaken  of  with 
impunity. 

(3)  Egypt. — Bread,  uncooked  vegetables,  beans  cooked  in  oil, 
cheese,  and  goats'  soured  milk  enter  largely  into  the  dietary 
of  the  people,  while  meat  is  partaken  of  only  sparingly. 

(4)  The  Malagasi  live  on  rice;  (5)  the  Kaffirs  chiefly  on  milk, 
maize,  millet,  and  yams.  Cereals  and  tubers  form  the  chief 
food  of  (6)  the  Negroes,  some  tribes  living  entirely  on  bananas, 
plantains,  and  cocoanuts.  Certain  pastoral  tribes  who  eat  meat 
and  drink  milk  are  prohibited  for  religious  reasons  from  using 
vegetables.  Fish  is  an  important  article  of  diet  on  the  banks 
of  the  great  African  rivers.  Cannibalism  is  still  practised 
among  certain  of  the  African  Negro  races,  and  among  the  Negroes 
of  the  western  parts  of  British  New  Guinea.  Human  flesh,  used 
as  food,  is  occasionally  indulged  in  in  the  region  of  the  Congo. 
It  is  not  safe  to  visit  some  of  the  native  villages  unless  properly 
guarded  and  well  armed. 

American. — (i)  The  Eskimos  (Eskimaux  derived  from  Wiyaski- 
mowok,  i.  e.,  raw  flesh  eaters),  in  their  savage  condition,  sub- 
sist almost  entirely  on  animal  substances.  At  times  they  eat 
roots,  berries,  and  reindeer  moss  and  seaweeds.  In  Danish 
Greenland  a  certain  amount  of  imported  food,  viz.,  bread, 
barley,  and  peas,  is  consumed.  When  food  is  abundant  the 
Eskimo  will  eat  as  much  as  ten  pounds  of  meat  and  fat  at  a 
single  meal.  Frozen  flesh  is  devoured  raw;  fresh  meat  is  boiled. 
The  blood  and  contents  of  the  stomach  of  the  reindeer  are 
added  as  articles  of  diet.  Blubber  too  is  valuable  as  a  food, 
being  used  as  fuel  and  lamp  oil  during  the  long  winter  months. 
The  natives  of  the  interior  of  Alaska  eat  fish,  ptarmigan,  susliks 
(or  gophers  or  chipmunks),  reindeer,  sea  lion,  harp  seal,  and 
whale — commonly  the  white  whale  or  Beluga  of  the  Arctic 
seas — and  occasionally  a  stranded  rorqual. 


THE  FOOD  OF  MAX  41 

(2)  The  Fitegians  live  almost  exclusively  on  a  shell-fish  diet. 
Dar\vin«  has  noted  that  their  staple  food  was  a  fungus  (Cyttaria 
Dani'inii). 

(3)  The  Xorth  American  Indians,  such  as  the  Sioux,  formerly 
used  the  flesh  of  the  bison  as  food,  the  skin  being  converted  into 
clothing  and  other  necessaries  of  Hfe. 

(4)  Among  the  Patagonians,  in  the  absence  of  farinaceous  food, 
marrow  and  fat  form  the  essential  articles  of  diet.  Blood  is 
on  all  occasions  eagerly  drunk.  Horse  flesh  is  considered  a 
luxury,  and  used  on  ceremonial  occasions. 

(5)  The  Indians  of  Mexico  seldom  employ  condiments  for 
flavouring  food,  which  is  generally  simple  in  character  and 
taken  cold.  The  magnificent  character  of  the  teeth  common  to 
their  race  is  undoubtedly  due,  as  pointed  out  by  Falero  (Dejital 
Cosmos,  vol.  xlvii,  Xo.  5),  to  the  fact  that  teeth  and  jaws 
only  are  used  in  eating  food.  Their  "teeth  are  real  knives, 
with  which  he  (the  Indian)  cuts  meat,  peels  sugar-cane,  cuts 
string,  or  picks  bones;  of  his  molars  we  can  say  that  they  are 
true  mills  which  pulverize  everything  that  comes  within  their 
reach." 

rvlELAXESiAX. — u)  Fijians  are  large  meat  eaters,  but  they  also 
consume  many  vegetable  materials,  such  as  taro,  yams,  sugar- 
cane,   cocoanuts,    etc. 

(2)  The  Maoris  eat,  as  staple  foods,  the  sweet  potato,  fern 
roots,  taro,  breads  made  from  the  bulrush  and  from  the  berries 
of  trees,  edible  seaweed,  fish,  and  birds.  Certain  gums  and 
bitumen  are  freely  chewed.  As  PickerilP«  remarks:  "I  have 
been  unable  to  gather  any  evidence  either  from  the  Maoris 
themselves  or  from  other  observers  that  they  ever  practised 
cleaning  the  teeth  by  any  artificial  means." 

(3)  Papuans  are  largely  vegetarian  in  their  diet,  but  are  partial 
to  the  flesh  of  pig.  wallaby,  and  a  large  tropical  beetle  which 
is  usually  eaten  raw.  With  regard  to  the  so-called  cannibalism 
which  is  found  in  New  Guinea,  a  recent  explorer,  Dr.  Lorenz. 
declares  that  the  Papuans  do  not  feed  on  human  flesh,  but 
there  exist  certain  tribal   ceremonies  at  which  the  heart  and 


42  THE  TEETH  AXD   THEIR  FUXCTIOXS 

brains  of  their  dead  enemies  are  consumed  in  order  that  the 

eater  may  secure  for  himself  the  courage  and  intellect  of  his 

slain  foe. 

The  nature  of  the  food  of  Man  is  an  important  factor  to  take  into 

consideration  when  dealing  with  the  problems  of  the  etiology  of  dental 

caries.     According  to  Pickerill/^  "a  large  consumption  of  meat  does 

not  confer  even  a  relative  immunity."     The  following  table,  compiled 

from   the   interesting   information   given   in   his    "The   Prevention   of 

Dental    Caries    and    Oral    Sepsis,"    shows,    at    a  glance,    the    average 

incidence  of  caries  in  the  relatively  immune  races  of  Mankind. 

Maoris 1-2%  Kaffirs i4-2% 

Eskimos i-4%  Bushmen 20.6% 

Northwest    American    Indians    (coast  Australian  Aborigines 20.5% 

tribes) 3-9%  Tasmanian  Aborigines 27.0% 

Polynesians 5  2  to  19*^ 

As  Factors  in  Facial  Development. — It  is  highl}-  probable  that  the 
development  and  growth  of  the  jaws  are  governed  b}'  the  important 
collective  functions  of  both  the  deciduous  teeth  and  their  successors, 
which,  according  as  they  are  well  or  ill  placed  in  their  respective  arches, 
are  able  to  impart  to  the  face  an  aspect  of  refinement  or  animalism, 
as  the  case  may  be.  A  study  of  this  question  is,  however,  wanting, 
and  definite  statements  cannot  yet  be  made  as  to  their  precise  role 
in  this  respect. 

The  Specific  Major  Functions  of  the  Teeth 

Speech. — Of  the  Specific  Major  Functions  of  the  Teeth,  the  highest 
is  speech — correct  articulate  speech, -^  the  enunciation  of  words. 

Salter'*  writes:  "The  teeth  constitute  an  essential  element  in  the 
organs  of  speech.  Without  them  the  precise  and  clear  pronunciation 
of  a  great  man^-  letters,  particularly  consonants,  would  be  impossible, 
and  the  resources  of  the  oral  cavity,  as  an  organ  of  speech  greatly 
circumscribed.  Accordingly  we  find  that  when  the  teeth  are  lost, 
certain  imperfections  in  articulation  are  immediately  entailed. 

"The  principal  way  in  which  the  teeth  assist  in  the  production  of 
articulate  sounds  is  by  acting  as  an  arch,  or  horse-shoe-shaped  ridge, 
within  which,  and  against  which,  the  tongue  may  act  as  a  valve,  and  by 


THE  SPECIFIC  MAJOR  FUXCTIOXS  OF   THE   TEETH 


43 


pressing  against  which,  it  may  produce  a  modified  and  variously  placed 
partial  or  complete  closure."  The  site  of  the  sound  is  not  when  the 
tongue  is  in  actual  contact  with  the  teeth,  but  when  it  is  not  in  perfect 
apposition.    Salter  has  constructed  the  following  physiological  alphabet: 


Articulate  sounds 


Vowels 

a terminally  dental 

e wholly  dental 

i terminally  dental 

0 not  dental 

u inceptively  dental 


Nasal 

m labio-nasal 

n dento-nasal 

«g palato-nasal 


Mutes 

(closure  complete) 


Soft 

b labial 

d dental 


Aspirate 

p labial 

; dental 


Semivowels 

(closure  incomplete) 


.  (hard)  palatal 


k palatal 


Oral 


A  s  pirate 

f denti-labial 

.J dental 

rh dental 

II dental 

ch  (English) ....  dental 
th  (in  through) .  .  dental 

sh dental 

ch  (German)  .  .  .palatal 


Soft 

V denti-labial 

2 dental 

r dental 

/ dental 

j dental 

(/;  (in  thoti)  .  .  .  .dental 
zh  (French  j) . .  .dental 


The  accompanying  diagram,  after  Salter,  is  intended  to  represent 
a  sagittal  section  of  the  vault  of  the  hard  palate,  the  soft  palate,  and 
the  tongue,  and  to  show  that  the  sounds  of  various  letters  are  produced 
intra-orally  by  the  positions  of  tongue,  teeth,  and  palate.  Thus  the 
sound  of  the  letter  K  is  produced  by  the  application  of  the  back  of 
the  tongue  to  the  soft  palate  and  back  teeth;  S  is  formed  on  placing 
the  tip  of  the  tongue  close  against  the  gum  behind  the  maxillary 
incisors,  and  Th,  by  carrying  it  further  forward  against  the  edge  of 
the  incisors  themselves  and  projecting  it  slightl}'  between  the  teeth. 

The  pronunciation  of  D  involves  the  firm  placing  of  the  tip  of  the 
tongue  against  the  gum  behind  the  maxillary  incisors,  its  edges  against 
the  lateral  alveolar  arches  and  teeth.     Complete  closure  ensues,  and 


44  THE  TEETH  AND  THEIR  FUNCTIONS 

the  letter  is  formed  when  the  parts  are  suddenly  separated.  More 
forced  breathing  similarly  produces  T.  In  N  exactly  the  same  obtains, 
but  the  sound  is  continued  through  the  nasal  passages.  When  a 
person  is  suffering  from  nasal  catarrh  which  somewhat  occludes  the 
nose,  the  pronunciation  of  N  is  as  if  it  were  sounded  ED.  In  cleft 
palate  extending  through  the  soft  tissues  and  the  uvula,  D  cannot  be 
sounded  at  all  for  this  reason. 

In  the  letters  F  and  V  the  lower  lip  is  brought  into  contact  with 
the  upper  teeth,  the  former  by  a  gentle,  the  latter  by  a  forcible  expira- 
tion. The  loss  of  a  single  incisor  materially  interferes  with  the  correct 
pronunciation  of  these  letters. 

Fig.  13 


tl,{Gultural) 


Outline  drawing  of  the  oral  parts  used  in  the  production  of  speech,  and  the  relation  of  the  tongue 
to  the  teeth  and  the  palate.  (After  Salter.)  {TH)  Position  for  pronunciation  of  TH;  (DS)  for 
"d,  "  closure  complete,  and  "  S,"  closure  incomplete;  (Ch)  as  in  Liebchen;  (Ch)  as  in  Scotch  och;  {K) 
for  "k"  and  "g"  hard. 

In  L,  the  closure  of  the  parts  is  in  the  middle  line  and  the  opening 
at  the  sides.  The  sound  is  obtained  by  applying  the  lingual  extremity 
firmly  against  the  gums  behind  the  maxillary  incisors  in  such  a  way 
as  to  leave  open  lateral  spaces,  and  is  generated  by  the  passing  of  air 
through  these  side  apertures. 

An  edentulous  person  can  speak  without  the  presence  of  teeth; 
but  it  is  extremely  likely  that  if  it  were  possible  for  a  person  to  be 
edentulous  from  birth  and  throughout  life,  the  pronunciation  of  the 
consonants  of  the  alphabet  and  of  certain  words  would  be  almost 
impossible.  The  following  interesting  case  exemplifies  this  point: 
A  patient,  aged  twenty-two  years,  who  is  believed  to  have  congenital 
absence  of  the  crowns  of  the  teeth,  and  whose  mouth  at  the  present 
time  exhibits  a  unique  appearance,  as  if  all  the  crowns  of  the  perma- 


THE  SPECIFIC  MAJOR  FUNCTIONS  OF   THE   TEETH  45 

nent  teeth  had  been  levelled  with  the  gum,  is  unable  to  pronounce 
such  words  as  "scissors,"  "thistle,"  etc.,  otherwise  than  as  if  they 
were  written  "thiththers,"  "thithle."  (See  Appendix.)  Therefore,  one 
uses  the  term  "Correct  Speech." 

The  teeth  are  not  employed  in  pronouncing  all  the  vowels.  It  is  the 
majority  of  the  consonants  which  are  produced  by  their  use.  Let 
the  reader  imagine  the  mouth  to  be  an  empty  box  during  the  pronuncia- 
tion of  the  letters  of  the  alphabet.  If  the  vis  a  tergo  of  the  respiratory 
apparatus,  acting  or  non-acting  upon  the  lid  of  the  box  (the  lips), 
closes  it  partially  or  completely,  it  follows  that  if  there  is  a  partial 
closure  of  the  door  (/.  e.,  the  lips)  the  aspirates  are  formed.  If  there 
is  a  complete  closure  the  explosives  are  formed.  Consonants  are, 
conveniently,  thus  divided  into  aspirates  and  explosives.^ 

According  to  Briicke,'-  who  differs  in  his  opinions  from  Salter, 
there  are  four  so-called  Articulation  positions  found  in  the  production 
of  speech: 

(i)  Between  the  lips.  (2)  Between  the  tongue  and  the  hard  palate 
and  the  front  teeth.  (3)  Between  the  tongue  and  the  soft  palate  and 
the  back  teeth.     (4)  Between  the  vocal  chords. 

Of  these  articulation  positions,  the  aspirates  F,  V,  and  W  are  formed 
between  the  lips;  the  letters  S,  Z,  and  L  are  produced  by  the  concerted 
action  of  the  tongue,  the  hard  palate,  and  the  front  teeth;  while  / 
represents  the  third  Articulation  position. 

Of  the  explosives,  the  first  Articulation  position  is  represented  by 
the  letters  B  and  P,  the  second  by  T  and  D,  while  the  third — that  is, 
between  the  tongue  and  the  soft  palate  and  the  back  teeth — produces 
the  letters  K  and  G. 

Table  of  Classification  of  the  Principal  Consonants. 

Articulation  Position.  Explosives.  Aspirates. 

1.  Labial,  partly  dental B.  P.  F.  V.  W. 

2.  Palatal,  lingual  and  dental T.  D.  S.  Z.  L.  Th.  Sch. 

3.  Buccal,  lingual  and  dental K.  G.  J.  Ch.* 

The  reader  is  also  referred  to  an  important  contribution  to  this 
subject  by  Oakley  Coles. ^ 

*"Th"  at  the  commencement  of  a  word  such  as  "their,"  "this,"  is  also  called  a  denti-Iingual. 


46  TEE  TEETH  AXD  THEIR  FUXCTIOXS 

Too  much  stress  must  not,  however,  be  placed  upon  the  functions  of 
the  teeth  in  the  pronunciation  of  letters.  As  Gutzmann'"  points  out: 
"Only  the  sibilants  (S,  Z,  Sch,  etc.)  are  frequently  affected  by  the 
more  serious  loss  or  malpositions  of  the  teeth;  but  these  impediments 
of  speech  can  generally  be  removed  by  constant  practice,  even  with- 
out any  attempts  at  the  regulation  of  their  position." 

Ornamentation. — Other  Specific  Major  Functions  of  the  Teeth  are 
Ornamentation,  and  in  connection  with  certain  Ethnic  Ceremonial 
Rites  and  Customs. 

It  is  obvious  that  to  the  civilized  mind  a  beautiful  set  of  teeth  is 
an  ornament  to  any  face.  Well-formed  and  well-kept  teeth  make  a 
plain  face  handsome,  almost  as  much  as  the  colour  of  the  hair  or  the 
brilliancy  of  the  eyes  or  the  character  of  the  skin. 

Curiously,  the  natives  of  foreign  lands  consider  that  mutilation  or 
staining  of  the  teeth  is  a  mark  of  ornamentation.  The  Annamese, 
for  instance,  paint  their  teeth  with  a  mixture  of  nutgalls  and  iron 
filings.  In  some  of  the  rural  districts  of  Japan,  married  women  and 
betrothed  girls  have  their  teeth  similarly  disfigured  with  betelnut 
juice,  probably,  in  this  case,  to  make  their  owners  unattractive  to  the 
opposite  sex.  The  Javanese  use  small  files  for  deforming  the  shapes 
of  their  teeth. 

In  the  jaws  of  young  males  of  the  Wagogo  tribes  of  German  East 
Africa  the  two  first  mandibular  incisors  are  chiselled  out,  for  one  or 
more  of  the  following  reasons:  As  an  ornamentation,  as  a  tribal  mark 
— as  testifying  to  his  powers  of  endurance  of  pain,  and  part  of  an  initia- 
tion ceremony — and  as  a  convenient  gap  for  purposes  of  feeding  in 
cases  of  threatened  lockjaw  after  tetanus.  A  skull  showing  this  mutila- 
tion, presented  by  the  author,  can  be  seen  in  the  Museum  of  the  Royal 
College  of  Surgeons  of  England.  A  similar  custom  obtains  today 
among  the  aboriginal  Australians.^^* 

*  Dr.  Duckworth'  has  given  a  careful  "  description  of  an  Ashanti  skull  with  defective  dentition" 
which  is  of  great  interest.  The  craniological  and  dental  features  of  a  skull  of  a  young  Ashanti  exhibits 
marks  of  quite  an  unusual  kind.  Ethnic  dental  mutilations  are  not  unknown  in  West  Africa,  but  it 
is  extremely  rare  to  find  the  maxillary  incisors  extracted,  and  still  more  rarely  all  four,  as  in  this 
specimen.  There  is  no  doubt  whatever  that  they  were  removed  by  artificial  means.  Sergi^"  shows 
that  the  practice  of  removing  incisor  teeth  is  characteristically  East  African.  Here  then  there  is  an 
example  of  a  great  exception.  The  author  last  named  found  in  some  rock-hewn  tombs  of  Abyssinia, 
referred  to  the  Fifth  Century,  A.D.,  that  complete  removal  of  all  the  maxillary  incisors  had  occurred 
in  seven  out  of  twenty-nine  crania  belonging  to  a  supposed  Hamitic  race. 


THE  SPECIFIC  MAJOR  FUNCTIONS  OF   THE   TEETH 


47 


The  practice  of  disfiguring  the  teeth  amongst  the  Indians  of  Yucatan 
and  Mexico  has  been  going  on  since  the  Sixteenth  Century,  although 
not  so  much  today  as  at  that  period.  They  used  to  saw  their  teeth 
into  various  shapes  and  drill  holes  in  them  for  the  purpose  of  beautify- 
ing the  looks  of  the  women. 

Fig.  14 


Skull  of  a  native  of  German  East  Africa.     X  4.    At  x  the  site  whence  the  mandibular  first  incisors 
were  knocked  out.     There  are  no  sockets  in  the  very  thin  alveolar  process.     Cf.  Fig.  96. 

The  filing  of  teeth  in  the  East  Indian  Archipelago  is  analogous, 
amongst  girls,  with  the  European  custom  of  "putting  up  the  hair" 
at  the  commencement  of  the  first  catamenial  period. 

Other  reasons  for  artificially  interfering  with  this  gift  of  Nature 
exist.      Dampier  describes  how  the  Australian  aborigines,  whom  he  met 


48  THE  TEETH  AND  THEIR  FUNCTIONS 

in  his  travels  at  the  end  of  the  Seventeenth  Century,  had  a  universal 
custom  of  removing  all  their  front  teeth.  Some  tribes  believed  that 
an  excessive  and  disastrous  rainfall  could  be  stopped  by  knocking 
out  their  teeth.  It  has  been  suggested  that,  by  this  wholesale  extrac- 
tion, the  reincarnation  of  the  persons  so  operated  upon  would  be 
assured.^  In  Queensland,  some  tribes  hold  the  belief  that  a  girl  whose 
front  teeth  have  been  extracted  gets  good  water  to  drink  when  she 
goes  to  Heaven,  otherwise,  if  she  retains  her  teeth,  she  has  nothing 
but  muddy  water.  As  the  late  Andrew  Lang  remarks:  "This  looks 
like  a  fable,  meant  to  reconcile  girls  to  the  loss  of  their  teeth,  which 
must  have  been  knocked  out  for  some  other  reason,  perhaps  merely 
as  a  visible  sign  that  they  had  passed  through  the  ceremonies  making 
them  marriageable." 

Howitt,"  in  a  singularly  fascinating  and  scholarly  work,  writes: 
"The  knocking  out  of  the  two  lower  middle  front  teeth  is  not  confined 
to  boys  only  (in  South  East  Australia).  When  a  child  is  from  eight 
to  twelve  years  of  age  the  teeth  are  taken  out  in  the  following  manner: 
Two  pieces  of  the  Kuya-mara  tree,  each  about  a  foot  in  length,  and 
chisel-shaped,  are  placed  on  either  side  of  the  tooth  to  be  extracted 
and  driven  tightly.  Some  wallaby  skin  is  then  folded  twice  or  three 
times  and  placed  on  the  tooth,  and  a  piece  of  wood  about  two  feet 
long,  being  placed  against  the  wallaby  skin,  is  struck  with  a  heavy 
stone.  Two  blows  suffice  to  loosen  the  tooth,  which  is  then  pulled 
out  by  the  hand.  This  is  repeated  with  the  second  tooth.  As  soon 
as  the  tooth  is  extracted,  a  piece  of  damp  clay  is  placed  on  the  gums  to 
stop  the  bleeding.  .  .  .  The  teeth  are  placed  inside  a  bunch  of 
emu  feathers  smeared  with  fat  and  are  kept  for  about  twelve  months, 
under  the  belief  that  if  they  were  thrown  away  the  eagle  hawk  would 
cause  longer  ones  to  grow  up  in  their  places,  which  would  turn  up  over 
the  upper  lip  and  thus  cause  death.  The  boy's  teeth  are  carefully 
kept  by  the  boy's  father,  and  long  after  the  mouth  is  healed,  he  dis- 
poses of  them  in  the  company  of  some  old  men  in  the  following  manner: 
He  makes  a  low  rumbling  noise,  not  using  any  words,  blows  two  or 
three  times  with  his  mouth,  and  then  jerks  the  teeth  through  his  hand 
to  a  distance.  He  then  buries  them  about  eighteen  inches  in  the  ground. 
The  jerking  motion  is  to  show  that  he  has  already  taken  all  the  life 


THE  SPECIFIC  MAJOR  FUNCTIONS  OF   THE   TEETH  49 

out  of  them,  as,  should  he  fail  to  do  so,  the  boj-  would  be  liable  to  have 
an  ulcerated  mouth  and  a  distorted  face.  This  is  another  instance 
of  the  belief  that  there  is  an  intimate  connexion  between  the  teeth 
and  the  person  from  whom  they  were  extracted,  even  at  a  distance, 
and  after  a  considerable  time." 

The  knocking  out  of  a  child's  canine  is  held  in  Northern  Formosa 
to  make  him  stronger  and  swifter  of  foot;  and  teeth  are  extracted 
during  seasons  of  mourning. 

In  Africa  and  x^ustralia  a  man's  tribe  is  often  recognized  by  the  cut 
of  his  teeth,  the  front  members  of  the  series  either  having  been  ground 
to  a  point  or  carved  away  in  an  angular  pattern. ^^  ^^  It  is  the  custom 
among  the  Rejangs — one  of  the  non-Malay  tribes  of  Sumatra — to 
mutilate  the  teeth,  which  are  either  filed  almost  level  with  the  gums 
or  sharpened  to  a  point. 

Extraction  and  mutilation  of  the  teeth  are  verj-  common  amongst 
the  tribes  of  Central  Africa  (Report  of  the  Wellcome  Research  Labora- 
tory, Khartoum,  191 1).  Livingstone  was  told  that  the  reason,  in  the 
Batoka  tribe,  was  that  they  wished  to  look  "like  oxen  and  not  like 
zebras."  Others  hold  that  the  sharpening  of  the  teeth  gives  the  owner 
a  ferocious  appearance,  that  it  distinguishes  man  from  monkey,  and 
that  it  may  exhibit  their  cannibalistic  proclivities.  The  teeth  (incisors) 
may  be  notched  on  their  mesial  surfaces  only,  or  on  both  their  mesial 
and  distal  surfaces,  being  either  ground  to  a  point,  or  remaining  blunt 
and  wedged  apart.  Examples  of  these  horizontal  slits,  or  reduction 
of  angles,  or  chipped  surfaces  of  half  the  teeth,  ma^^  be  found  amongst 
the  various  designs  adopted  by  these  peoples,  and  the  lower  teeth  are 
more  commonly  removed  than  the  upper  (Figs.  15  to  20). 

To  other  extraordinary  ethnic  disfigurements  it  may  be  added  that 
the  habit  of  blackening  the  teeth,  similar  to  that  which  obtains  in  French 
Indo-China,  is  universally  found  in  Melanesia,  from  the  Admiralty  Isles 
to  the  New  Hebrides.  Familiarity  has  produced  an  admiration  for 
its  effects,  and  has  initiated  an  intense  dislike  to  the  possession  of 
white  teeth  like  "those  of  a  dog."  The  natives  are  in  the  habit  of 
mixing  together  and  chewing  assiduously  areca  nut,  lime,  and  betel 
pepper  leaf,  the  result  being  the  accumulation  of  a  black  incrustation 
on  the  surfaces  of  the  teeth. 
4 


50 


THE  TEETH  AND  THEIR  FUNCTIONS 


The  teeth  of  certain  mammals,  such  as  those  of  the  wolf,  the  sperm 
whale,  etc.,  form,  when  collected  and  strung  together  like  beads,  a 

Fig.  15  Fig.  16 


Mutilation  of  maxillary  incisors.     Type  I. 
(The  Avungara,  or  Royal  House.) 

Fig.  17 


Mutilations  of  maxillary  incisors.    Type  III. 
(The  Avungara,  or  Royal  House.) 

Fig.  19 


Mutilation    of    incisors.      Type    V.     (The 
Zandeh  Nyam-nyam  tribe.) 


Mutilations  ot  maxillary  mcisors.     Type 
II.     (The  Avungara,  or  Royal  House.) 

Fig.  18 


Mutilation  of  incisors.      T3'pe  IV.^  (The 
Zandeh  Nyam-nyam  tribe.) 

Fig.  20 


Ethnic  mutilations  involving  the  re- 
moval of  the  mandibular  first  incisors. 
Type  VI.  (The  Makrakka  and  Bagaro 
tribes  ) 


mark  of  ornamentation  in  a  different  sense  to  that  already  detailed. 
Thus,  the   fishermen  of  Naples  and   some  of  the  inhabitants  of  the 


THE  MINOR  FUNCTIONS  OF   THE  TEETH  51 

East  End  of  London  wear  teeth  for  the  dual  purposes  of  ornamenta- 
tion and  "to  ward  off  the  evil  eye."  The  natives — both  men  and 
women — of  Fiji  and  other  islands  array  themselves  with  armlets  and 
necklets  of  rows  of  teeth — such  as  those  of  the  sperm  whale. 

Emotional  Expression. — Another  Specific  Major  Function  of  the 
Teeth  is  as  a  Means  for  Expressing  the  Emotions. 

This  occurs  by  the  rapid  elevation  of  the  lip  and  the  uncovering  of 
the  teeth,  chiefly  the  upper  canines.  The  act  of  sneering  and  the  act 
of  defiance  produce  certain  movements  of  the  muscles  of  the  upper 
lip,  which  draw  up  the  angles  of  the  mouth  and  display  the  teeth. 
Annoyance  on  the  part  of  a  person  is  often  accompanied  by  the  undue 
exhibition  of  the  teeth.  The  emotion  of  rage,  especially  in  the  insane 
and  in  epileptic  idiots,  emphasizes  this  fact  remarkably  well.  Not  only 
are  the  lips  raised  and  they  become  exposed,  but  sometimes  they  are 
protruded  and  sometimes  retracted,  both  these  attitudes  probably  being 
remnants  of  a  habit  acquired  during  prehistoric  times,  when  our  simian 
forefathers  fought  their  enemies  with  their  incisors  and  canines.  The 
faculties  of  laughing  and  broad  smiling  are  accompanied  by  the  laying 
bare  of  the  upper  teeth.  Curiously  enough,  however,  as  Darwin^ 
points  out,  this  does  not  occur  in  the  chimpanzee.  Jealousy  and  terror 
in  the  lower  animals  are  accompanied  by  a  similar  exhibition;  anger, 
also,  as  in  the  long-tailed  monkeys  and  the  baboons.  Pleasure,  as 
expressed  by  a  fondled  ape,  shows  itself  by  the  exposure  of  the  teeth, 
as  also  does  the  grinning  or  the  snarling  of  dogs. 


The  Minor  Functions  of  the  Teeth 

Although  this  division  is  an  arbitrary  one,  it  is  convenient  to 
describe  the  less  important  natural  offices  that  the  teeth  collectively 
are  called  upon  to  fulfil,  as  exemplified  in  fishes,  reptiles,  and  mammals. 
They  include  (I)  the  prehension  of  food;  (II)  for  sexual  warfare; 
(III)  for  the  purposes  of  transport  and  locomotion;  (IV)  as  weapons 
of  offence;  (V)  for  purposes  of  toilet;  (VI)  as  chisels;  (VII)  as 
mechanical  protections  to  the  eyes;  (VIII)  for  sifting  food;  (IX) 
as  sound-producing  organs;   (X)   for  attacking  prey. 


52 


THE   TEETH  AND   THEIR  FUNCTIONS 


The    Prehension   of    Food. — Two    examples   out   of   many   may   be 
mentioned :     The  pike  has  a  few  large  recurved  teeth  anchylosed  to  the 


A  B 

The  teeth  of  a  common  pike  (ii50.\- /wcjMi) .     X  j.     ^,  upper  jaw;  S,  mandible. 

margin  of  the  lower  jaw  in  addition  to  numerous  smaller  ones,  dis- 
tributed elsewhere  (Fig.  21).     By  means  of  the  former  the  fish  is  able 

Fig.  22 


Head  of  a  true  dolphin  (Delphiniis 


securely  to  grasp  its  slippery  living  prey.     The  mouth  of  the  dolphin, 
in  the  mammalian  group,  too,  presents  a  good  example  of  organs  which 


THE  MINOR  FUNCTIONS  OF   THE   TEETH 


53 


perform  this  function  (Fig.  22) — a 
function  which  obtains  very  largely 
throughout  the  natural  world. 

For  Combative  Purposes.  — 
Many  illustrations  might  be 
given;  it  is  sufficient  to  say  here 
that  in  the  Mammalia  these  func- 
tions exist  exclusively.  Thus  the 
adult  male  narwhal,  an  aberrant 
species  of  dolphin  called  also  the 
sea  unicorn,  has  one  tusk  —  a 
maxillary  incisor.  Generally,  the 
left  one  is  present,  and  has  a 
spiral  twist  throughout  its  course. 
It  may  be  twelve  feet  long,  and 
its  curves  wind  from  right  to  left. 
The  rudiments  of  the  right  incisor 
are  seldom  developed,  probably 
because  this  side  of  the  skull  is 
smaller  than  the  left,  a  fact  clearly 
seen  in  a  specimen  in  the  Museum 
of  the  Royal  Dental  Hospital  of 
London.  The  animal  is  a  native 
of  the  Arctic  regions,  and  feeds  on 
small  fish,  cephalopods,  and  crus- 
taceans (Fig*.  23). 

Another  example  of  teeth  used 
for  sexual  warfare  is  found  in  the 
canines  of  the  male  musk  deer 
(Fig.  24).  This  small  creature 
possesses  no  antlers,  but  what  he 
lacks  for  the  purpose  of  defence  and 
offence  on  his  head  he  possesses  in 
his  mouth.  The  musk-deer  lives 
in  the  mountains  of  Central  Asia, 
in  Thibet,  China,  and  Siberia. 


Male. 


Female 


Skulls  of  a  male  and  female  narwhal  {Monodon 
monoceros) ,  viewed  from  above.  X  ir-  Usually 
the  male  has  but  one  (the  left)  tusk,  the  right 
being  undeveloped. 


54  THE  TEETH  AND  THEIR  FUNCTIONS 

A  further  instance  may  be  given  in  the  mandibular  incisors  of  the 
Indian  rhinoceros,  who  fights,  not  with  his  horns,  as  is  generally 
believed,  but  with  his  teeth.  The  English  horse  occasionally  uses 
his  incisors  for  the  same  purpose. 

Fig.  24 


Skull  of  a  male  musk  deer  (Moschus  moschiferus).      X  i- 

For  the  Purposes  of  Transport  and  Locomotion. — In  India  it  is 
not  an  uncommon  thing  to  see  the  elephant  transporting  from  place 
to  place  bales  of  goods  or  piles  of  timber  by  means  of  his  tusks. 
The  beaver,  with  the  help  of  his  chisel-like  incisors,  carries  the  scaf- 
folding for  his  home  on  the  banks  of  the  river  for  considerable 
distances  (Fig.  25).  The  domestic  cat  carries  her  kittens  from  place 
to  place  by  means  of  her  teeth;  and  the  Indian  of  Mexico  makes  many 
uses  of  his  teeth  and  jaws  as  a  third  hand  for  holding  the  reins  of  his 
horse,  supporting  his  clothing  and  fire-arms  while  fording  rivers, 
and  graduating  the  weight  of  loads. 

The  walrus  is  said  to  use  its  canine  teeth  for  dragging  itself  out 
of  the  water  on  to  the  ice  floes  in  the  North  Pacific  Ocean  and  the 
polar  regions  of  the  Atlantic  Ocean.  It  is  enabled,  by  means  of  its 
powerful  tusks,  also,  to  dig  out  of  the  mud  certain  molluscs  on  which 
it  principally  feeds."     It  also  eats  starfishes,  sandworms,  and  shrimps." 

Allied  to  this  function  is  that  of  anchorage,  as  exemplified  in  the 
extinct  Dinotherium ,  a  mammal  which,  although  living  in  Pleistocene 
times,   may  today  be  classified  among  the  Perissodactyle  ungulates, 


THE  MINOR  FUNCTIONS  OF   THE  TEETH 


55 


midway  between  the  tapir  and  the  elephant.  (See  Chapter  XVI.) 
This  mammal  had  aquatic  habits,  like  the  hippopotamus.  The  tusks 
correspond  to  or  are  homologous  with  incisors.  The  symphysis  of 
the  mandible  is  prolonged  and  deflected  downwards,  carrying  two 
incisors,  which  are  two  feet  in  length,  being  larger  in  the  male  than  in 
the  female.  By  means  of  these  the  animal  was  enabled  to  anchor 
itself  to  whatever  it  wished. 

Fig.  25 


Skull  of  a  beaver  [Castor  fiber) 


The  chisel-shaped  incisors  are  deeply  pigmented. 


As  Weapons  of  Offence. — The  teeth,  amongst  certain  groups  of 
animals,  are. largely  used  for  killing  their  prey  or  killing  their  enemies. 
This  is  well  exemplified  in  the  viperine  snakes,  where  the  teeth  are 
so  modified  as  to  become  poisonous  fangs,  in  contra-distinction  to  the 
pythons,  who  kill  their  prey  by  crushing  it  in  the  coils  of  their 
bodies. 

A  remarkable  instance  of  the  teeth  being  used  for  the  purpose  of 
destroying  its  foes  is  presented  b>'  the  Siberian  mammoth,  which 
roamed  over  the  Northern  Hemisphere  thousands — perhaps  four 
hundred  thousand  years  ago.  The  body  of  one  of  these  huge  extinct 
animals  was  discovered  in  1901,  and  is  to  be  found  in  the  Museum  of 
the  Academy  of  Sciences  at  St.  Petersburg.^"    It  is  a  unique  specimen, 


56  THE  TEETH  AND   THEIR  FUNCTIONS 

inasmuch  as  not  only  fossil  remains  were  found,  but,  on  account  of 
its  being  frozen  in  the  glacial  mud  of  the  Siberian  Sea,  the  hair  and 
the  wool  and  other  soft  parts  have  been  retained.  The  stomach  con- 
tained some  undigested  food,  and  grass  was  found  between  the  molars. 
It  is  believed  that  this  particular  Russian  specimen  met  its  death  by 
sinking  into  a  grave  of  sand  and  clay,  from  Avhich  it  was  unable  to 
emerge,  which,  on  becoming  flooded  and  frozen,  retained  its  buried 
occupant  for  hundreds  of  centuries. 

The  Texan  mammoth  —  that  is,  Elephas  imperator  —  measured 
fourteen  feet  six  inches  in  length,  the  animal  standing  fifteen  feet  high. 
Similarly  to  the  Siberian  mammoth  it  used  its  incurved  tusks  (incisors) 
for  killing  its  enemy  by  hurling  it  into  the  air.  Most  of  the  non- 
human  prey  of  this  ancestor  of  the  modern  elephant  possessed  in 
those  preglacial  times,  protective  armour  over  their  bodies.  It  was 
impossible,  therefore,  for  their  larger  enemies  to  kill  them  in  any 
other  way  than  by  throwing  them  into  the  air  and  smashing  their 
protective  armour  on  the  rocks. 

For  the  Purposes  of  a  Comb. — An  interesting  little  creature — the 
Flying  Lemur  of  India  and  the  Malay  Peninsula,  called  the  Galeo- 
pithecus  volans — is  said  to  use  its  mandibular  incisors  as  a  comb  for 
cleaning  its  fur.  These  incisors  are  pectinate  in  form,  and  constitute 
an  admirable  instrument  for  toilet  purposes.  The  Galeopithecus 
belongs  to  the  insectivorous  animals,  although  it  eats  leaves  and  fruits, 
and  is  not  one  of  the  Primates,  with  which  it  used  to  be  classified.  It 
attains  to  the  size  of  a  cat,  and  has  a  lateral  expansion  of  the  skin 
of  the  body,  supported  by  the  limbs  and  tail,  which  when  extended 
forms  a  patagium,  by  Avhich  means  it  floats  through  the  air  in  a  down- 
ward direction.  The  pectinate  incisors  of  the  flying  lemur  are  analogous 
with  the  epithelial  papillae  on  the  upper  surface  of  the  tongue  of  the 
cat,  that  is  to  say,  both  these  different  organs — the  incisors  and  the 
papillae — are  used  for  performing  the  same  function,  namely,  cleaning 
the  fur  (Fig.  26).  The  pectiniform  mandibular  teeth  of  the  hyrax 
are  not  so  complex  in  character  as  those  of  the  former.  Their  use  is 
unknown.  Allied  to  this  function,  attention  may  be  drawn  to  the 
outermost  of  the  eight  lower  anterior  teeth  of  the  giraffe.  This  tooth, 
which  is  bilobed,  is  used  by  its  possessor  as  a  comb  for  removing  leaves 


THE  MINOR  FUXCTIOXS  OF   THE   TEETH 


57 


of  trees  without  doing  harm  to  the  young  twigs.  A  deer,  in  browsing, 
eats  all  leaves  and  young  twigs  of  branches,  but  the  giraffe  carefully 
avoids  damaging  the  trees  themselves. 


J^l^-^ 


Skull  of  a  flying  lemur  {Galcopithecus  volatis),  showing  its  pectinate  mandibular  incisors.      X  xV 

Chiselling. — Rodent  animals,  like  the  squirrel,  porcupine  (Fig.  27), 
and  rat,  possess  chisel-shaped  teeth,  with  which  the  former  fracture 

Fig.  27 


Skull  of  a  porcupine  (Hystrix  cristala).     X  \.    The  molars  in  this  genus,  as  in  those  of  the  old 
world  generally,  are  only  partially  rooted. 

the  hard  shells  of  nuts.  The  Balistcs,  or  tile-fish  of  tropical  seas,  has 
incisiform  teeth  for  boring  holes  in  the  hard  shells  of  molluscs  in  order 
to  extract  the  soft  parts.     The  pearl  oysters  in  the  fisheries  of  Ceylon 


58 


THE  TEETH  AND  THEIR  FUNCTIONS 


are  thus  attacked.  It  is  interesting  to  note,  parenthetically,  that  the 
oyster  has  other  enemies  besides  Man  and  these  carnivorous  fishes. 
The  common  starfish  of  our  British  coasts  prey  upon  the  oyster;  and 
although  it  takes  a  weight  of  seven  pounds  to  produce  mechanical  arti- 
ficial opening  of  the  shells  of  this  bivalve,  the  starfish  can,  by  constant 
pulling  on  each  shell,  gradually  exhaust  the  power  of  the  muscle  of 
the  foot  of  the  oyster  and  force  the  shells  apart.  It  is  said,  too,  that 
the  octopus,  which  is  unable  to  exercise  such  pressure  on  the  shell  of 
the  oyster,  because  of  its  great  disparity  in  size,  waits  until  the  mollusc 
opens  its  shell  voluntarily,  and  that,  at  that  moment,  it  places  a  pebble 
in  the  space  thus  produced,  an  action  which,  of  course,  prevents  the 
closing  of  the  shells. 


S^-'-V 


Skull  of  a  male  babirussa  of  the  island  of  Celebes  (Baljiniaa  al funis).      X  I-    The  maxillary 
canines  are  placed  extra-orally. 

As  Protections  to  the  Eyes. — The  curvatures  of  the  upper  and  lower 
canine  teeth  of  the  wild  pig  and  boar  (Fig.  28)  found  in  the  Malay 
Archipelago  are  so  constituted  as  to  form  a  protection  to  the  eyes 
when  the  animal  is  seeking  food  in  the  bush.  The  presence  of  these 
huge  tusks  prevents  any  injury  occurring  by  any  of  the  fallen  boughs 
or  trunks  of  trees.*     So  curved  do  these  lower  canines  become  that, 

*  This  statement  is  doubted  by  Wallace  ("Malay  Archipelago,"  vol.  i),  who  believes  that  they  are 
monstrous  overgrowths  occurring  in  the  male  sex  only,  as  females  who  similarly  hunt  for  their  food 
do  not  possess  them. 


THE  MINOR  FUNCTIONS  OF  THE  TEETH  59 

persistently  growing,  in  some  instances  they  may  ultimately  form  a 
circle;  so  much  so,  that  the  natives  of  New  Guinea  break  off  the  upper 
tusks  of  the  wild  boar  to  allow  the  lower  ones  room  for  this  growth 
into  circular  form.  When  the  development  is  complete  the  animal  is 
slain  and  the  teeth  are  used  as  armlets  for  jewelry  and  other  decora- 
tive purposes. 

As  Sieves. — Amongst  the  chsetodonts — a  genus  of  coral  fishes  of 
the  tropical  seas  living  in  the  neighbourhood  of  coral  reefs — which 
are  both  carnivorous  and  insectivorous  in  type,  the  teeth  are  found 
to  act  as  a  sieve.  They  are  very  long,  numerous,  and  slender,  very 
thickly  placed,  and  afford  an  example  of  the  dents  en  velours  in  the 
mouth  of  fishes.  The  chsetodont  is  able  to  sift,  from  a  mouthful  of 
water,  the  essential  parts  of  its  food,  like  the  whalebone  whale, 
but  by  different  means.  It  may  be  mentioned  that  a  small 
coral  fish,  Toxotes  jaculator  by  name,  is  able  to  project  from  the 
surface  of  the  river  in  which  it  lives  a  stream  of  water  on  to 
flies  which  are  hovering  over  it,  thus  drowning  them.  It  is  said 
that  the  natives  of  the  Malay  Archipelago  keep  this  fish  in 
aquaria  in  captivity  for  the  purpose  of  watching  it  perform  this 
trick. 

As  Sound-producing  Organs. — Some  naturalists  have  given  the 
name  of  the  "drum"  to  Pogonias — a  fish  found  on  the  coasts  of  the 
United  States.''  They  believe  it  is  enabled  to  produce  the  sound,  by 
the  rapid  clapping  together  of  large  molariform  teeth  found  on  the 
pharyngeal  bones.  Travellers  on  anchored  steamers  imagine  they  can 
■detect  these  sounds  in  the  stillness  of  the  night.  Little  is  known 
as  to  the  actual  cause;  by  some  it  is  thought  to  be  due  to  the  fish 
beating  their  tails  on  the  keels  of  the  ships,  so  as  to  get  rid  of  certain 
parasites  attached  to  their  bodies.  Other  observers  also  state  that 
the  sunfish  and  the  Balistes  are  able  to  produce  sounds  in  their 
mouths. 

For  Attacking  Prey. — Lastlj',  the  rostral  teeth  of  sawfish  (Pristis) 
(Fig.  29) — structures  entirely  different  and  far  removed  from  the 
oral  organs — are  used  for  the  purpose  of  tearing  open  the  abdomens 
of  large  whales  and  soft-bodied  fish  of  the  greater  seas  and  oceans. 
The  rostrum  provided  with  the  teeth  acts  as  a  veritable  saw,  while 


60 


THE  TEETH  AND   THEIR  FUNCTIONS 


the  oral  teeth  are  concerned  in  the  mastication  of  the  intestines  of 
the  prey,  thus  being  used  in  the  same  way  as  the  teeth  of  many  other 
fashes. 

Fig.  29 


Rostrum  of  sawfish  {Pristis) 


At  X  a  socket  of  a  tooth  has  been  exposed. 


FUNCTIONLESS    TEETH 

Some  teeth  are  probably  functionless  with  regard  to  mastication 
or  comminution  of  food,  namely,  those  on  the  branchial  arches  of 
whales — as  in  the  Selache  maxima  of  the  Northern  hemispheres  and 
the  British  coasts — and  also  on  the  osseous  gill  arches  of  the  sun- 
fishes. 


SUBSTITUTES    FOR    TEETH 

Other  organs  may  act  in  the  same  way  as  teeth;  for  instance,  the 
spinal  processes  of  the  under  surface  of  the  vertebrae  in  Dasypeltis 
scabra,  an  egg-eating  colubrine  snake  of  South  Africa.  This  is  a  small 
snake,  which  crams  relatively  large  hens'  eggs — which  are  crushed 
as  they  traverse  the  oesophagus — into  its  mouth,  and  may  become  so 
inflated  as  to  resemble  a  small  football  with  a  tail  attached  to  it.-* 
Probably  the  reason  it  takes  the  unbroken  egg  into  its  mouth  is  to 
prevent  waste  of  food. 


APPLICATION  OF  DENTAL  FUNCTIONS   TO  THE  PURPOSES  OF  ART     Gl 

The  hard  sheaths  which  form  the  cases  for  the  jaws  of  the  turtle 
or  tortoise,  homologous  with  the  beaks  of  birds,  and  the  jaw-bones 
themselves,  as  in  the  Sphenodon,  also  subserve  the  masticating  func- 
tions of  the  teeth.  The  latter,  also  known  as  the  Tuatera,  and  com- 
monly, but  incorrectly,  regarded  as  a  lizard,  found  inhabiting  two  small 
islands  off  the  coasts  of  New  Zealand,  displays  a  unique  type  of  denti- 
tion, inasmuch  as  young  individuals  possess  in  the  front  of  each  jaw 
a  pair  of  chisel-shaped  teeth,  followed  behind  by  a  double  row  of  closely 
placed  small  teeth,  separated  by  a  groove,  into  which  a  single  man- 
dibular series  passes  when  in  use.  In  old  creatures  the  lower  teeth 
become  worn  away,  and  the  edge  of  the  jaw  itself  highly  polished  and 
employed  for  dental  purposes.^ 

THE  APPLICATION   OF  DENTAL  FUNCTIONS  TO  THE 
PURPOSES    OF    ART 

Nature  and  Art  are  often  closely  allied  in  the  matter  of  the  shapes, 
structure,  and  uses  of  the  teeth.  Civilized  and  barbaric  man,  observ- 
ing these  functions,  have  utilized  the  principles  of  their  construction 
and  methods  of  employment  in  inventing  and  producing  domestic 
and  other  articles  for  every-day  service.  Inasmuch  as  it  is  most  prob- 
able that  the  recognition  of  the  character  of  the  sutures  of  the  human 
skull  gave  origin  to  the  invention  of  dovetailing,  adopted  in  the 
manufacture  of  wooden  boxes,  so  teeth  have  also  furnished  examples 
for  copy  b^  mankind. 

Probably  the  most  striking  and  the  closest  of  all  these  adaptations 
is  that  of  the  poison  fang  of  the  viperine  snakes.  Here  is  essentially 
a  surgical  instrument  for  the  infliction  of  a  punctured  wound — and 
the  injection  into  that  wound  of  a  deadly  fluid — which  is  provided 
with  a  canal  which  terminates  near  but  not  at  its  extremity.  The 
surgeon  has  used  the  principle  of  the  structure  of  the  poison  fang 
for  the  invention  of  the  hollow  needle  of  the  modern  hypodermic 
syringe.    (See  Fig.  65.) 

Further,  the  millstone  probably  owes  its  origin  to  the  shape  and 
functions  of  the  molar  of  the  elephant;  the  teeth  and  jaws  of  the  skate 
{Myliobatis)  gave  rise  to  the  invention  of  the  crushing  mill  and  roller; 


62  THE  TEETH  AND  THEIR  FUNCTIONS 

the  jaws  of  the  wolf-fish  to  the  nut-cracker;  the  incisors  of  the  hippo- 
potamus to  the  steel  adze  of  Europe  and  the  stone  adze  of  Polynesia; 
the  incisors  of  the  beaver  to  the  chisel;  the  tusks  of  the  walrus  to  the 
scaling  fork  {Stiirmgabel)  in  use  in  Sixteenth  Century  warfare,  and 
at  the  present  day  as  an  ice  anchor  or  grappling  hook  in  the  Arctic 
or  Antarctic  regions;  the  jaws  of  the  shark  to  the  deer  trap  of  India; 
the  jaws  of  the  dolphin  to  the  rat  trap;  the  jaws  of  the  snake  to 
the  "throwing  stick"  of  New  Caledonia;  and  the  rostrum  of  the 
sawfish  to  the  spears  and'  wooden  swords  armed  with  sharks'  teeth 
employed,  even  today,  by  the  natives  of  Australia  and  the  inhabitants 
of  Mexico." 

References 

1.  "Animal  Life  and  the  World  of  Nature,"  1903. 

2.  Bland-Sutton.     "Tumors,  Innocent  and  Malignant,"  1906. 

3.  Brooke-NichoUs.     "The  Teeth  of  Australian  Animals,  "  1908. 

4.  Catalogue  of  the  Natural  History  Museum,  South  Kensington. 

5.  Oakley  Coles.     "On  the  Production  of  Articulate  Sound  (Speech),"  Trans.  Odonto.  Soc,  Great 
Britain,  vol.  iv,  new  series. 

6.  Darwin.     "The  Expression  of  the  Emotions  in  Man  and  Animals,"  1872;  "The  Voyage  of 
H.  M.  S.  Beagle,"  1840. 

7.  Duckworth.    Journal  of  Anatomy  and  Physiology,  igi2. 

8.  Eccles  and  Hopewell-Smith.    "Dermoid  Teeth,  or  Teeth  Developed  in  Teratomata, "  Proc^ 
Roy.  Soc.  of  Medicine,  1912. 

9.  Frazer.    "The  Golden  Bough,  "  1911,  third  edition. 

10.  Gutzmann.     "Ueber  die  Wertigkeit  der  inneren  Mundteile  (Zunge,  Zahne,  Gaumen)  fiir  die 
physiologische  Lautbilding, "  Trans.  V  Inter.  Denial  Congress,  1911. 

11.  Howitt.    "The  Native  Tribes  of  Southeast  Australia,"  1904. 

12.  Kirke.    "Handbook  of  Physiology  (Halliburton),"  1900. 

13.  Lubbock.    "Ants,  Bees,  and  Wasps, "  1888. 

14.  Owen.    "Odontography,"  1840.     "The  Comparative  Anatomy  and  Physiology  of  the  Verte- 
brates," 1866,  vol.  i. 

15.  "P.  H.,"  in  "The  Sphere,"  1902. 

16.  Pickerill.    "The  Prevention  of  Dental  Caries  and  Oral  Sepsis,"  1912. 

17.  St.  George  Mivart.    "Types  of  Animal  Life, "  1894. 

18.  Salter.    "Dental  Pathology  and  Surgery, "  1874. 

19.  Schmeil.    "Handbuch  d.  Zoologie,"  1901. 

20.  Sergi.    "Atti  de  la  Societa  Romana  di  Anthropologic,"  1908. 

21.  Shattock.     "Acardiac  Acephalous  Ovarian  Embryoma, "  Trans.  Path.  Soc,  London,  1907. 

22.  "The  Living  Races  of  Mankind,"  vol.  i;  edited  by  H.  N.  Hutchinson  and  R.  Lydekker,  1906. 

23.  Thomas.    "The  Natives  of  Australia,  "  1906. 

24.  Tomes.    "A  Manual  of  Dental  Anatomy,"  1908. 

25.  Tylor.    "Anthropology,"  1881. 

26.  Werner.    "The  Natives  of  British  Central  Africa, "  1906. 

27.  J.G.Wood.    "  Nature's  Teachings, "  1903. 


CHAPTER    III 
GENERAL   NUMERATION   AND   TOPOGRAPHY 

The  Numbers  of  the  Teeth  in  Fishes,  Reptiles,  and  Mammals. — Their  General  Osseous  Relation- 
ships.— Dental  Notations. — The  Typical  Mammalian  Formula. — The  Numerical  Reduction 
in  Man. — Theories  Regarding  the  Incisors. — The  Factors  in  the  Production  of  the  Diminu- 
tion in  Number. — Instances  of  Redundancy  and  Deficiency. 


NUMBER    OF    TEETH 

Following  up  the  train  of  thought  already  indicated  in  Chapter  I, 
and  arguing  again  "from  the  known  to  the  unknown,"  it  would  seem 
that  the  number  of  teeth  in  the  lower  animals  and  in  Man  should 
now  engage  the  attention  of  the  reader.  The  number  of  teeth  in  the 
human  mouth  is  generally  more  or  less  obvious  to  all.  In  dealing  with 
the  question,  the  study  begins  with  the  toothed  vertebrates,  and  con- 
siders the  fishes  first,  then  the  reptiles,  and  finally  the  mammals. 
This  is  the  order  of  Creation,  and  is  followed  in  these  pages  through- 
out. The  dentitions  of  fishes  will  be  only  slightly  glanced  at,  and 
those  of  reptiles  also,  the  main  point  being  the  characteristics  of  the 
teeth  of  Man. 

It  is  important  to  note  that  teeth  are  not  classified  into  incisors, 
canines,  etc.,  as  Anatomists  usually  speak  of  them,  in  the  fishes  and 
reptiles.  The  reason  of  this  will  be  apparent  at  once  when  the  defini- 
tions and  significance  of  these  terms  are  realized.  Roughly  to  differ- 
entiate the  teeth  in  the  mouth  of  a  fish  or  reptile  one  describes  them 
as  "front  teeth,"  or  "back  teeth,"  or  "pharyngeal  teeth,"  or  "lingual 
teeth,"  according  to  their  situation. 

Fishes. — Generally  speaking  the  jaws  are  elongated  and  narrow 
to  accommodate  a  vast  number  of  teeth.  In  Hemiramphus  (Fig.  30) 
the  mandible — itself  toothless — is  of  great  length  to  enable  this  fish 
to  shovel  up  into  its  mouth  crowds  of  aquatic  worms  and  insect  larvae, 
on  which  it  subsists,  from  the  sandy  shores  of  the  rivers  which  it 
^   inhabits. 


64 


GENERAL  XUMERATIOX  AXD   TOPOGRAPHY 


In  this  class  the  number  of  teeth  varies  very  considerably.  In- 
stances are  found  where  they  are  entirely  absent,  as  in  the  pipe-fish 
and  the  Hippocampus  (Fig.  31).  These  fishes  probably  live  on  small 
annelids  (worms)  and  require  no  dental  armament  for  the  purpose  of 
comminuting  their  food.  In  the  myxine  and  the  Bdellostoma  one 
single  tooth  is  found,  situated  on  the  median  line  of  the  palate.  It 
has  been  pointed  out  in  Chapter  II  that  the  exposed  surface  of  this 
tooth  is  corneous,  having  beneath  it  a  small  cap  of  enamel  and  dentine. 
There  are  other  teeth  in  the  mouths  of  the  pike  and  the  Bdellostoma, 


Fig.  30 


Head  of  Hemiramphus. 


A,  mouth  closed;  B,  mouth  open. 


situated  on  the  lingual  bones  which  partake  of  the  nature  of  dents 
en  cardes.  In  the  Ceradotus  there  are  two  small  chisel-shaped  maxillary 
and  two  mandibular  ridged  plates,  the  two  lower  being  larger  than  the 
upper.  These  probably  partake  more  of  the  nature  of  bone  than  of 
the  character  of  teeth.  The  Ceratodns  (Fig.  32)  is  interesting  as  being 
probably  the  connecting  link  between  the  fishes  and  the  amphibians 
(frogs  and  toads).  It  is  the  so-called  lung  fish  of  Australia,  may  attain 
the  length  of  six  feet,  lives  amongst  mud  and  dead  leaves,  and  rises 
at  intervals  to  the  surface  to  breathe.  The  settlers  of  Queensland 
have  named  it  the  Burnet  River  salmon. 


NUMBER  OF   TEETH 


65 


These  are  instances  of  fishes  which  possess  few  teeth  or  none 
but   between   these   two   groups   and    the   fishes   which    present 
numbers  of  teeth,  there  are  count- 
less variations.     The  pike  {Esox  ^^°-  i- 
li(ciiis)  possesses  enormous  num- 
bers of  teeth,  which  are  practi- 
cally incomputable.    In  its  mouth 
examples  of  dents  en  brasses,  dents 
en  cardes,  and  also  dents  en  velours 
are  found. 

Fig.  31 


at  all; 
Qreat 


The  sea-horse  {Hippocampus),  belonging  to 
the  Family  SyngnathidcB,  of  Sub-order  11 
(Dophobranchii),  of  Sub-class  III  (Teleostomi), 
of  Class  V  {Pisces).     X  -}. 


Jaws  of  the  Australian  lung-fish  {Ceratodus), 
of  Sub-class  I  {Dipnoi),  of  Class  V  {Pisces). 
X  !•  ^'  upper  jaw;  5,  lower  jaw,  showing 
the  dental  plates. 


Reptiles. — Amongst  the  reptiles,  the  number  of  teeth  is  never  so 
great  as  in  the  fishes,  nor  so  small  as  in  some  mammals  and  the  fishes 
abo\'e  named.  Generally  speaking,  the  number  is  not  fixed  so  as  to  be 
characteristic  of  any  class;  thus  Varaniis  (Fig.  33),  the  monitor  lizard, 
has  about  sixteen  upper  and  fourteen  lower  teeth.  The  batrachian, 
Triton  cristatus  (a  newt)  has  many  teeth  on  the  superior,  inferior, 
pre-maxillary,  and  vomer  bones,  the  latter  being  extremely  small. 

Mammals. — With  regard  to  the  mammals:  the  whales,  that  is  to 
sav,   the  toothed    whales,    the    Odontoceti,  afTord    the    fewest   number 


66  GENERAL  NUMERATION  AND  TOPOGRAPHY 

of  teeth.  For  instance,  the  beaked  whales  ("Bottle-nose"  whales 
of  the  English  coasts)  have  one  pair  of  teeth  in  the  mandible, 
which  are  invisible  during  the  fresh  condition.  There  is  a  Bottle-nose 
whale  named  the  Hyperoodon  rostratus,  which  is  frequently  stranded 
on  the  British  coasts.  Its  length  is  usually  about  thirty  feet,  and 
it  yields  oil  and  spermaceti.  In  this  mammal  the  pair  of  teeth  is 
situated  in  the  front  of  the  mandible;  whereas,  in  the  Mesoplodon 
(a  "beaked"  whale,  fifteen  feet  in  length)  they  are  situated,  as  the 
name  implies,  in  the  middle  of  the  jaw.  In  the  Natural  History  branch 
of  the  British  Museum,  Kensington,  there  is  a  specimen  of  Mesoplodon 
layardi,  which  shows  these  two  teeth  enormously  grown,  curving 
over  the  upper  jaw,  so  as  almost  to  prevent  the  mouth  from  being 

Fig.  33 


Skull  of  a  monitor  lizard  [Varamis).      X  |. 

fully  opened.  They  are  strap-like  in  shape.  The  narwhal,  as  has 
already  been  described,  has  two  tusks.  Arnux's  whale  (the  Berardius 
arnuxi),  of  the  New  Zealand  waters,  possesses  two  pairs  of  lower 
teeth,  while  the  Grampus  griseus  has  two  teeth  at  each  side  of  the 
mandible.  They  become,  in  old  individuals,  reduced  in  number  to  one 
on  each  side  of  the  lower  jaw. 

Amongst  the  Marsupials  there  are  two  mammals  which  possess 
a  small  number  of  teeth:  for  instance,  the  Tarsipes,  a  small  rat-like 
animal,  which  is  insectivorous  and  nectar-eating,  with  a  long  prehensile 
tongue,  has  the  lower  incisors  procumbent,  and  a  few  small  teeth 
opposed  to  them  in  the  maxilla.  The  Australian  water-rat  (Hydromys) 
possesses  only  twelve  teeth. 

Generally    speaking,    rodents    have    twenty    teeth.      The    two-toed 


NUMBER  OF  TEETH 


67 


sloth  (Fig.  318)  has  eighteen,  and  it  is  monophyodont.  Man,  and  the 
apes  of  the  Old  World,  i.  e.,  Africa,  etc.,  such  as  the  gorilla,  have 
thirty-two   teeth    (Fig.    34).      The   New  World    (American)    monkeys 


Fig.  34 


The  teeth  of  an  adult  man.      X 
Fig.  35 


Skull  of  a  chimpanzee  {Anthropopithecus  troglodytes).     X  j.     The  third  maxillary  molars  are 
smaller  than  either  of  the  others. 


68  GENERAL  NUMERATION  AND  TOPOGRAPHY 

possess  thirty-six  (Fig.  36).  An  excessive  number  of  teeth  is  found  in 
the  common  porpoise,  where  ninety  dental  organs  exist.  The  Gangetic 
dolphin,  which  lives  in  the  fresh  water  of  the  Ganges,  Brahmaputra, 
and  Indus  Rivers,  possesses  one  hundred  and  twenty  teeth.  It  is 
difficult,  at  first  sight,  to  account  for  this  huge  number  of  teeth  in 
a  mammal,  particularly  one  adapted  to  aquatic  habits;  but  when  it 
is  recalled  that  this  dolphin  is  quite  blind  and  has  to  grope  about 
at  the  bottom  of  the  rivers  for  small  fish,  it  will  be  found  that  Nature 

Fig.  36 


Skull  of  a  New  World  monkey  (Cebus) 


There  are  three  pairs  of  premolars  in  each  law. 


has  beautifully  adjusted  means  to  an  end  by  providing  it  with  a  large 
number  of  teeth.  The  true  dolphin  may  have  more,  the  number 
varying  from  one  hundred  to  one  hundred  and  ninety.  Again,  there  is 
a  beneficent  example  of  Nature  in  providing  this  creature  with  ample 
means  for  obtaining  its  food.  The  greatest  number  of  all,  however, 
is  reached  by  a  fresh-water  dolphin  which  inhabits  the  Rio  de  la  Plata. 
Of  all  mammals  it  has  the  greatest  number  of  teeth,  namely,  about 
two  hundred  and  fifty. 


OSSEOUS    RELATIONSHIPS 

In  Fishes. — Teeth  may  vary  in  position  or  situation.     The  Teleostei, 
or  bony  fishes,  present  an  important  dental  armament.     It  is  necessary 


OSSEOUS  RELATIONSHIPS  69 

to  note  the  names  and  positions  of  the  bones  which  form  the  walls,  floor, 
and  roof  of  the  mouth  of  these  fishes,  for  it  will  be  seen  later,  with 
regard  to  the  bones  of  the  skull  of  the  snake,  and  with  regard  to  the 
development  of  the  human  jaws,  that  a  knowledge  of  the  bones  form- 
ing the  reptilian  and  the  piscine  skull  is  essential. 

The  upper  margin  of  the  mouth  is  bounded  by  the  right  and  left 
Pre-maxillaries  above,  which  are  frequently  tooth-bearing  bones; 
above,  and  parallel,  are  the  right  and  left  Maxillaries.  The  lower 
margin  is  bounded  by  the  Pre-mandibulars  or  Dentary  bones.     The 

Fig.  37 


Diagram  of  the  bones  of  the  head  of  a  teleosteous  fish.  (After  Giinther.)  Pm,  the  premaxilla; 
M,  the  maxilla;  D,  the  dentary;  A,  the  articular  and  the  angular;  Q,  the  quadrate;  Pi,  the  pterygoid 
and  palate;  Po,  the  praeoperculum. 

roof  is  formed  by  the  Vomer  in  the  middle,  articulating  with  the  Basi- 
sphenoid,  and  bounded  laterally  by  the  Palatine,  the  Pterygoid  and 
Ento-pterygoid.  The  floor  is  formed  by  the  Lingual  bones,  which 
form  a  median  longitudinal  plate,  to  the  sides  of  which  are  attached 
the  lower  bones  of  the  pharyngeal  arches.  i\rticulating  with  the 
Maxillary  bones  are  the  Pre-orbital  above,  and  the  Angular  and 
Articular  below.  The  Angular  articulates  with  the  Quadrate,  and 
the  Pre-orbital  with  the  Pre-frontal  and  Turbinal.  The  mandible 
of  a  fish,  such  as  the  perch,  consists  of  the  Dentary,  Articular, 
and    Angular  bones  (Fig.  37).      In    addition  to  this,   the    pharj'n.x  is 


70 


GENERAL  NUMERATION  AND  TOPOGRAPHY 


strengthened  by  the  presence  of  one  to  six  or  more  Pharyngeal  bones 
above  and  below.^ 

The  situations  of  the  Dental  Systems  in  fishes  is  interesting.  Thus, 
in  the  perch,  the  Pre-maxillaries  and  the  Dentary  are  the  only  bones 
which  carry  teeth.  In  the  roach  and  the  barbel,  the  Pharyngeal 
bones  alone  have  teeth  placed  upon  them.  In  the  Lahrus  and  Scarus, 
they  are  found  on  the  Pre-maxillary,  Pre-mandibular,  and  Pharyngeal 
bones.  Amongst  the  sharks  and  rays  (Fig.  38),  which  have  cartil- 
aginous skeletons,  they  are  placed  upon  the  maxillary  cartilage.      It 


Fig.  38 


Jaws  of  one  of  the  rays,  showing  sexual  differences  in  the  shapes  of  the  teeth.     The  jaws  are 
widely  distended.      X  |. 


has  already  been  pointed  out  that  in  the  mouth  of  the  pike  great 
numbers  of  teeth  exist;  and  it  will  suffice  now  to  say  that  they  are 
situated  on  the  Vomer,  the  Palatine,  the  Lingual,  the  Pre-maxillar}^ 
and  the  Dentary  bones. 

As  examples  of  irregular  positions  of  the  situation  of  teeth,  it  may 
be  mentioned  that  the  Pristis,  or  sawfish,  has  them  on  the  rostrum; 
the  lamprey  on  the  lips,  the  myxine  on  the  centre  of  the  palate,  and  the 
Myliohatis  (Fig.  39)  across  the  symphysis  of  the  lower  jaw. 


OSSEOUS  RELATIONSHIPS 


71 


In  Reptiles. — The  situation  of  the  teeth  in  the  reptiles  and  batra- 
chians  is  much  simpler.  There  may  be,  generally  speaking,  four: 
(i)  On  the  jaws  only,  as  in  the  crocodile,  and  many  lizards — for  instance, 
\"aranus — while  in  the  snakes — the  adder,  for  instance — they  are 
absent  from  the  Pre-maxillary  bones,  and  from  the  lower  jaws  of 
frogs,  but  they  are  present  on  both  the  upper  and  lower  jaws  of  the 
newt;  (2)  on  the  jaws  and  Pterygoid  bones,  as  in  the  iguana  and  the 
chameleon;  (3)  on  the  Palatine  and  Pterygoid  bones,  as  in  the  serpents 
and  the  viperine  snakes;  and  (4)  on  the  Vomer,  as  in  the  Batrachia 
generally. 

Fig.  39 


Jaws  of  the  eagle  ray  [Myliobatis) ,  showing  the  flat,  poUshed,  hexagonal  teeth,  and  the  cartilages 
in  which  they  are  imbedded.     Development  proceeds  from  within  outwards.      X  j. 

In  Mammals. — It  is  obvious  that  in  the  Mammalia  teeth  are  found, 
as  a  rule,  attached  to  the  margins  of  the  jaws.  A  few  exceptions 
exist,  however;  for  instance.  Echidna,  the  spiny  ant-eater — a  mono- 
treme  of  Australia,  New  Guinea,  and  Tasmania — is  edentulous  (Fig. 
326).  This  curious  creature  possesses  a  muzzle,  which  is  an  elongated 
slender  beak,  enclosing  a  long  extensile  vermiform  tongue.  On  the 
Pterygoid  bones,  as  well  as  on  the  tongue,  there  are  spines  of  an  epithe- 
lial character.  The  Echidna  is  nocturnal  in  its  habits,  lives  in  rocky 
and  sandy  districts,  and  rapidly  burrows  into  the  earth  on  the  approach 
of  danger.     Its  food  is  ants. 

Again,  the  South  American  ant-eaters  have  no  teeth;  the  tongue  is 


72  GENERAL  NUMERATION  AND   TOPOGRAPHY 

covered  with  viscid  saliva  from  the  maxillary  glands,  which  causes 
the  ants  from  an  ant-hill  to  adhere  to  it.  The  Great  Ant-eater,  terres- 
trial in  its  habits,  and  living  in  the  swampy  forests  of  South  America, 
is  also  edentulous,  and  the  arboreal  Tamandua,  or  Lesser  Ant-eater, 
similarly  devoid  of  teeth.  Again,  the  Scaly  Ant-eater  (Manis),  which 
resembles,  at  first  sight,  a  reptile,  is  edentulous.  This  animal  is  found 
in  South  Eastern  Asia  and  Ethiopia — Africa  south  of  the  Desert  of 
Sahara.^-  Amongst  the  mammals,  also,  it  must  be  noted  that  in  the 
Mystacoceti  or  baleen  whales — whalebone  whales — there  are  rudi- 
mentary teeth  which  are  very  early  shed.  Whalebone  is  interesting 
because  its  matrix  morphologically  corresponds  with  enamel,  being 
produced  by  a  cornification  of  the  epithelial  coverings  by  vast  numbers 
of  vascular  papillae,  which  are  long  thread-like  processes,  arising  from 
persistent  pulps  and  penetrating  the  hard  substance  of  the  whalebone 
plates.  In  the  whalebone  whales,  which  are  quite  distinct  from  the 
toothed  whales  already  noticed,  these  plates  hang  down  from  the  roof 
of  the  mouth  transversely  to  its  long  axis,  and  extend  nearly  along 
its  whole  width.  In  the  middle  line,  similar  plates  are  found.  The 
plates  act  like  a  sieve,  forming  a  series  of  parallel,  narrow,  elongated, 
triangular  laminae,  their  inner  edges  being  frayed  out  into  a  fringe. 
The  longest  plates  in  the  Greenland  whale  measure  twelve  feet,  and 
number  three  hundred  and  eighty.  In  the  Rorquals  the  length  is  a 
few  inches.  Baleen  whales  do  not  require  teeth  for  the  purpose  of 
alimentation,  for  they  eat  pteropods,  molluscs,  and  very  small  fishes, 
on  account  of  the  narrowness  of  the  oesophagus  for  the  passage  of 
larger  fish.^^ 

Sir  Harry  Johnstone"  writes:  "The  'right'  whales  open  their  mouths 
when  they  find  themselves  in  the  middle  of  shoals  of  minute  crustaceans 
and  pteropods,  and  then  close  the  mouth,  forcing  out  the  water  through 
the  sieve  of  the  whalebone.  The  tiny  organisms  that  are  prevented 
from  escaping  by  the  fringe  of  the  baleen  plates  then  fall  on  to  the 
broad  tongue  which  lies  in  the  great  hollow  of  the  under  jaw,  and  in 
this  manner  are  swallowed  through  the  very  narrow  gullet.  In  the 
'right'  whales  the  throat  is  so  narrow  at  the  swallow  that  it  would 
probably  allow  nothing  to  pass  of  larger  size  than  a  mouse.  When  the 
mouth  is  shut,  the  long  fringes  of  whalebone  fold  backward,  the  front 


DENTAL  NOTATIONS  73 

plates  lying  below  the  hinder  ones,  so  that  in  a  sense  the  long  ends 
of  the  whalebone  are  partially  contained  within  the  approach  to  the 
gullet.  When  the  animal  opens  its  mouth  widely,  the  whalebone 
springs  forward  till  it  is  perpendicular." 

The  whalebone  whales  include  five  classes:  (i)  The  BalcEiia  (right 
whales),  of  Greenland  and  Spitzbergen,  in  which  the  baleen  is  long 
and  black;  (2)  the  Neo-balcena,  of  New  Zealand  and  Australia,  in  which 
the  baleen  is  long  and  white;  (3)  the  grey  whale  of  the  North  Pacific, 
a  rare  mammal,  in  which  the  baleen  is  short  and  yellow;  (4)  the 
Megaptera,  or  hump-backed,  so-called  because  it  lies  sometimes  on 
its  side  in  the  water,  the  body  being  submerged,  and  extends  upwards 
a  flipper  which  is  bright  white  in  colour,  and  may  rise  to  a  height 
of  ten  feet  above  the  surface  of  the  water;  and  (5)  the  Bale^toptera, 
or  rorqual,  "finned  whales,"  "finned  backs,"  and  "razor  backs." 
Amongst  this  genus  is  the  most  gigantic  of  all  animals,  the  Balcenoptera 
sibbaldi,  which  reaches  a.  length  of  eighty  feet,  and  is  found  in  the  seas 
between  Scotland  and  Norway. 

Sufficient  has  been  said  here  to  show  the  great  characteristics  of 
the  two  classes  of  whales.  Both  at  first  have  rudimentary  teeth. 
In  the  Odontoceti  these  grow  and  persist,  while  in  the  baleen  whales 
they  are  shed,  and  the  mammal  remains  edentulous.  (See  Chapter 
XVI.) 

DENTAL    NOTATIONS 

The  number  of  the  teeth  in  any  given  Mammalian  dentition  is 
expressed  by  what  is  known  as  a  dental  formula..  There  are  several 
ways  of  graphically  depicting  such  a  formula.  Taking  collectively 
the  type  of  dentition  found  in  Man,  and  dealing  with  one  side  of  the 
skull  only,  this  may  be  simply  written  as  follows: 

Incisors  i  Canine  \  Premolars  f  Molars  |  X  2  =  32.  That  is,  there 
are  altogether  in  each  jaw,  four  incisors,  two  canines,  four  pre- 
molars, and  six  molars.  It  is  also  convenient  to  express  the  members 
of  the  deciduous  or  "milk"  series  in  small  type,  as  i.  c.  pm.  and  m. 
To  indicate  whether  a  tooth  belongs  individually  to  the  maxillary 
or  mandibular  bones,  one  writes,  for  example,  Pm-  for  the  second  left 


74  GENERAL  NUMERATION  AND  TOPOGRAPHY 

maxillary  premolar,  ^Pm  for  the  second  right  maxillary  premolar,  Pm2 
for  the  second  left  mandibular  premolar,  and  2Pm  for  the  second  right 
mandibular  premolar.  Similarly,  the  maxillary  and  mandibular  teeth 
of  either  side  may  be  represented  by  placing  a  numeral  above  or  below 
the  other  indicating  them,  thus: 

12  I      2      I       2        3 

I,  I,  C,  P,  P,  M,  M,  M     and     1,  I,  C,  P,  P,  M,  M,  M. 

12  I     2       I       2       3 

Clinically  it  is,  in  addition,  of  service  to  use  the  following  Symbols 
for  the  permanent  teeth. 

87654321  I  12345678 


87654321I12345678 

N 

and  for  the  deciduous  series: 

e  d    c  b  a     |     a  b  c  d  e 
edcba     i     abcde 

The  typical  number  of  Eutherian  teeth  is  forty-four.  An  extinct 
mammal,  named  the  Homalodontothermm,  possessed  the  typical  number, 
namely,  forty-four.  ^^  They  represented  transitional  stages  in  regard 
to  shape,  that  is  to  say,  the  third  incisor  was  rather  like  a  canine, 
the  first  premolar  was  rather  caniniform  also,  the  fourth  premolar  being 
molariform;  so  a  gradual  transition  from  incisors  to  canines,  then  to 
premolars  and  molars,  was  observed  in  the  jaws  of  this  mammal." 

The  Otocyon  megalotis,  a  curious  aberrant  member  of  the  dog  family, 
of  South  and  East  Africa,  a  kind  of  fox  with  long  ears — as  the  name 
implies — has  an  additional  molar  above  and  below  on  either  side, 
making  forty-eight  teeth  entirely."  This  is  an  example  of  the  greatest 
number  of  teeth  in  a  heterodont  placental  animal.'' 


NUMERICAL    REDUCTION    IN    THE    HUMAN    DENTITION 

Man  has,  in  normal  conditions,  thirty- two  teeth;  there  is,  therefore, 
a  considerable  reduction  from  the  typical  mammalian  formula." 
Which  teeth  are  absent?     The  third  incisor  and  the  first  and  second 


NUMERICAL  REDUCTION  IN   THE  HUMAN  DENTITION  75 

premolars  are  said  to  be.  It  is  probable  that  the  first  and  second  pre- 
molars are  suppressed  from  the  series,  as  it  is  the  rule — except  in  the 
polyprotodont  marsupials — that  when  premolars  are  missing,  the  first 
two  of  the  series  disappear.  There  is,  however,  some  doubt  as  to 
whether  it  is  the  third  incisor  which  has  disappeared  in  the  course  of 
evolution  from  the  mouth  of  the  immediate  ancestors  of  Man.*"  Those 
naturalists  who  favour  the  transitional  theory,  such  as  Hensel,  and  who 
take  the  Homalodontotherium  as  a  type,  consider  that  it  is  the  third 
incisor  which  has  gone,  for  there  is  no  resemblance  whatever,  from 
the  point  of  view  of  shape  or  size,  between  the  second  incisor  and 
the  canine.  Baume^  and  H.  H.  Edwards'*  hold  that  the  first  incisor 
is  the  absent  tooth. 

Albrecht^  (and  he  is  supported  by  Sir  Wm.  Turner^^  and  A.  Wilson'"), 
however,  considers  that  it  is  the  second  incisor  which  is  missing.  He 
believes  that  the  premaxillary  bones  are  developed  from  two  centres 
of  ossification,  that  there  are,  therefore,  four  premaxillary  bones  alto- 
gether. The  boundaries  of  the  premaxillary  bones  are  said  to  be  as 
follow:  In  front,  the  median  suture  of  the  superior  maxillae;  behind,  a 
suture  passing  between  the  second  incisor  and  the  canine  in  front,  and 
ending  in  the  anterior  palatine  canal.  But  this  German  observer 
believes  that  there  are  two  sutures,  one  on  the  distal  surface  of  the 
first  incisor,  the  other  on  the  mesial  surface  of  the  canine,  which  sepa- 
rates the  ectognathic  and  mesognathic  parts,  and  as  already  pointed 
out,  thinks  that  there  are  two  centres  of  ossification  for  each  premaxil- 
lary bone  (Fig.  40).  He  further  considers  that  the  osseous  division 
in  cleft  palates  runs  along  the  first-named  suture,  that  is,  the  one 
between  the  first  and  second  Incisor.  Therefore,  the  argument  is  that 
the  second  Incisor,  as  we  speak  of  it,  is  really  a  pre-canine  or  the  third 
Incisor.  Cases  have  been  rarely  recorded  of  tripartite  palates,  which 
carried  four  incisors  on  the  premaxillary  bone,  and  another  incisiform 
tooth  (pre-canine)  existed  also  beyond  the  cleft.  If  the  definition  of 
the  maxillary  incisors,  as  given  later,  be  accepted  as  teeth   implanted 

*  It  is  important  to  note  the  fact  that  neither  has  prehistoric  man,  nor  have  any  of  the  anthropoid 
apes,  lemurs,  or  bats,  ever  possessed  six  incisors  in  each  jaw.  Tlie  "disappearance"  of  a  third  incisor, 
or  the  "suppression"  of  the  two  anterior  premolars,  does  not  here  imply  the  existence  of  these  teeth, 
as  they  have  never  been  evolved. 


76 


GENERAL  NUMERATION  AND   TOPOGRAPHY 


in  the  premaxillary  bone,  the  conclusion  that  the  "pre-canine"  is 
the  same  as  the  third  incisor  of  the  normal  mammalian  dentition  is 
arrived  at,  and,  therefore,  that  the  lost  incisor  in  man  is  probably  the 
second  incisor. 

Fig.  40 


Palate  of  a  child,  aged  about  five  and  a  half  years,  in  which  the  maxillary  and  premaxillary  sutures 
remained  patent.     X  jV-    Each  premaxillary  bone  consists  of  two  portions,  and  carries  an  incisor. 

Variations  in  Number  of  Teeth. — Instances  of  the  numerical  defi- 
ciency and  redundancy  of  teeth  are  frequentl}^  encountered  in  prac- 
tice.    They  occur  more  commonly  in  the  upper  than  the  lower  jaw. 


Fig.  41 


Fig.  42 


Model  of  mouth  of  a  boy  having  six 
permanent  incisors.  The  canines  are  just 
erupting.  X  jo-  Original  in  the  posses- 
sion of  Mr.  Sidney  Spokes. 


Photograph  of  the  mouth   of  a  man,   showing 
seven  maxillary  incisiform  teeth. 


Incisors. — Fig.  41  is  a  photograph  of  a  plaster  cast  of  the  mouth 
of  a  boy  showing  six  well-formed  maxillary  incisors,  the  original  in  the 
possession   of   Mr.   Sidney  Spokes;   and  Fig.   42  that  of  a  man,  aged 


NUMERICAL  REDUCTION  IN   THE  HUMAN  DENTITION  77 

twenty-eight  years,  who  had,  in  the  superior  inter-canine  region, 
implanted  in  the  premaxillary  bones,  seven  teeth — all  fully  erupted 
and  the  majority  well  formed.  The  plaster  casts  and  photographs 
show  the  actual  condition.  From  an  examination  of  the  jaw  it 
was  evident  that  the  inter-canine  region  was  exceedingly  broad;  it 
measured  no  less  than  34  mm.,  while  the  mandibular  inter-canine 
region  measured  18  mm.  The  normal  adult  measurements  are  about 
28  mm.  in  the  upper  and  18  mm.  in  the  lower  jaw.  It  is  obvious 
that  both  the  ectognathion  and  the  mesognathion  are  broader  on 
the  right  than  on  the  left  side,  accommodating  four  teeth  to  the 
■other  three.  It  is  very  difficult  to  interpret  the  condition  and  cor- 
rectly name  the  teeth.  Morphologically  they  would  appear  to  be 
the  right  first  and  second  incisors,  a  third  incisor  (the  pre-canine 
of  Sir  William  Turner)  and  a  supernumerary  first  incisor,  all  in  the 
right  premaxilla;  and  in  the  left,  the  left  first  and  second  incisors,  and 
a  supernumerary  first  incisor.  It  would  seem  as  if  Nature  having  a 
wider  space  to  fill  than  usual  had  filled  up  the  gap  by  supplying  this 
person  with  an  extraordinary  number  of  teeth.  Rosenberg,^"  who  at 
the  end  of  the  last  century  collected  an  enormous  amount  of  literature 
on  the  subject,  and  inspected  large  collections  of  skulls,  plaster  casts 
of  the  mouth,  etc.,  considered,  in  spite  of  the  opinions  of  Mrchow  and 
Busch,  that  every  supernumerary  tooth  covered  with  enamel  was 
atavistic.  Rosenberg's  reading  of  the  condition  presented  by  this 
case  would  be  the  first  Incisor,  having  on  its  distal  surface  the  second 
Incisor,  and  on  its  mesial  surface  Incisor  alpha,  and  Incisor  gamma 
on  the  distal  surface  of  the  second  Incisor,  on  the  right  side;  and  on 
the  left.  Incisor^  and  Incisor,-  with  Incisor  beta  in  between.  The 
formula  would  read: 

yl,    =1,    'I,     al,     r.     1,3,     p. 

The  second  maxillary  incisors  are  often  undeveloped,  although  they 
may  have  existed  in  the  deciduous  dentition.  The  accompanying 
radiographs  of  a  boy,  aged  fifteen  years,  exemplifies  this  point  (Figs. 
43  and  44). 

Canines. — More  rarely  are  the  canines  absent  (not  so,  however, 
according  to   Berten^),  and   more   rarely  still   is  there  duplication  of 


78 


GENERAL  NUMERATION  AND  TOPOGRAPHY 


this  tooth.  A  remarkable  instance  is  seen  in  Figs.  47  and  48,  which  are 
radiographs  of  the  jaws  of  a  woman,  aged  twenty-seven  years.  The 
left  mandibular  canine  is  absent  while  the  right  mandibular  tooth, 
which  is  only  partially  erupted,  has  beneath  it  and  lying  horizontally 
with  its  crown  placed  toward  the  premolars,  a  second  canine. 


Fig.  43 


Fig.  44 


Radiograph  showing  absence  of  the  left 
maxillary  second  incisor. 


Radiograph  showing  absence  of  the  right 
maxillary  second  incisor. 


Premolars  and  Molars.  —  Further  illustrations  may  be  given 
showing  absence  of  the  right  mandibular  second  premolar  in  a  girl, 
aged  fourteen  years  (Fig.  77). 


Fig.  45 


Fig.  46 


Radiograph  showing  absence  of  left 
maxillary  canine. 


Radiograph  showing  absence  of  right 
maxillary  canine. 


In  Figs.  49  and  50,  all  four  second  premolars  and  the  left  maxillary 
second  incisor  are  missing  from  the  jaws  of  a  child,  aged  between  five 
and  six  years.     Calcification  of  the  third  molars  has  not  yet  commenced. 

For  additional  examples  of  anomalous  dentitions  the  reader  is 
referred   to  the  important  work  of  de  Terra.  ^^ 

It  has  been  already  noted  that  Man  in  normal  circumstances  has 
thirty-two  teeth.     The  third  molar  which,   as  an  outcome  of  racial 


NUMERICAL  REDUCTION  IN   THE  HUMAN  DENTITION 


79 


evolution  acting  in  a  threefold  manner  to  be  presently  described,  is 
gradually  being  lost  in  European,  Asiatic,  and  American  races.  It 
is  abundantly  evident  that  in  those  peoples  whose  teeth  are  most  fully 
functional  the  third  molars  are  not  only  erupted  earlier  in  life  than 

Fig.  47 


Radiograph  of  the  jaws  of  an  adult,  aged  twenty-seven  years.     Right  side.     See  also  Fig.  48. 

elsewhere,  but  that  they  reach  their  highest  state  of  development. 
Thus,  in  Mexico  this  tooth  begins  to  erupt  at  the  age  of  eighteen,  in 
the  mouths  of  Indians  and  half-breeds,  and  this  is  seldom  associated 
wdth    pathological    disturbances,    proceeding    on    purely    physiological 


80  GENERAL  NUMERATION  AND  TOPOGRAPHY 

lines.      Probably  the  Mexican  Indians  of  Yucatan,  Campeachy,  etc. 
with  a  few  African  tribes,  have  the  finest  teeth  in  the  world. 

Fig.  48 


Radiograph  of  the  jaws  of  an  adult,  aged  twenty-seven  years.     Left  side.     See  also  Fig.  47. 

Factors  in  the  Causation  of  Numerical  Reduction. — The  reader  is 
now  led  to  ask:  "  How  is  it  that  Man,  ?.  e.,  the  prehistoric  ancestor  of 
Man,  has  lost  from  his  mouth  an  incisor  and  two  premolars  in  each 
half  of  his  jaws?"     The  numerical  reduction  of  teeth  in  the  higher 


NUMERICAL  REDUCTION  IN   THE  HUMAN  DENTITION  81 

animals  is  probably  due  to  three  important  factors,  which,  all  or 
severally,  bring  about  a  reduction  in  the  number.  These  are  probably 
as  follow: 

Fig.  49 


Radiograph  of  the  jaws  of  a  child,  aged  about  six  years.     Right  side.    The  original  in  the  possession 
of  Mr.  W.  H.  Dolamore. 

(i)   Incomplete  evolution,  and,  therefore,  loss  of  function  of  organs. 
For  instance,  there  is  a  great  tendency  at  the  present  day  in  the  mouths 

6 


82 


GENERAL  NUMERATION  AND  TOPOGRAPHY 


of  men  for  the  third  molars  to  disappear.     Many  people  never  erupt 
this  tooth.     It  is  an  example  of  an  organ  which  is  not  required  under- 


FiG.  50 


Radiograph  of  the  jaws  of  a  child,  aged  about  six  years.    Left  side.     The  original  in  the  possession 
of  Mr.  W.  H.  Dolamore. 

going   degeneration,    and    finally    almost    disappearing.      As    another, 
there  may  be  instanced  the  Platysma  myoides,  and  also  the  vermiform 


NUMERICAL  REDUCTION  IN   THE  HUMAN  DENTITION  83 

appendix,  which,  in  Man,  is  rudimentary,  as  compared  to  the  same 
organ  in  the  rabbit.  The  nictitating  membrane  of  the  eye  of  birds 
remains  today  in  Man  as  a  mere  fold — the  plica  semilunaris : 

(2)  Progressive  enlargement  of  the  more  actively  functional  pre- 
molars and  molars;  for  instance,  in  the  cat  tribe — Felidce.  This  prob- 
ably has  been  brought  about,  through  their  position  in  the  dental  arch 
with  regard  to  the  attachment  of  the  very  powerful  masticating  muscles 
over  the  zygoma  of  the  jaws.  The  enormous  differences  in  the  size,  and 
shape,  and  occlusion  of  the  first  and  fourth  premolar  in  the  Felidce  is 
truly  remarkable,  and  probably  can  only  be  accounted  for  in  this  w^ay, 
that  is,  the  dynamic  forces  which  act  on  the  bone  through  exceptionally 
strong  muscular  movements,  producing  very  large  teeth;  and 

(3)  The  shortening  of  the  entire  jaw,  which  increases  the  power  of 
the  bite,  but  at  the  same  time  results  in  the  crowding  out  of  the  dental 
arch  of  those  teeth  which  can  be  most  readily  spared.  Comparison 
of  the  jaws  of  the  dolphin  and  of  the  chimpanzee  shows  this  at  once. 

Amongst  present-day  animals,  a  typical  mammalian  dentition  of 
forty-four  teeth  is  found  in  the  mole,  in  the  pig,  and  in  the  young  horse 
(Fig.  308).  In  the  latter,  the  first  premolar  is  lost  at  an  early  age, 
but  the  ordinary  adult  horse  has  the  whole  of  the  forty  teeth. 

References 

1.  Albrecht.    "Bec-de-lievre,"  Societe  d'anthropologie  de  Bruxelles,  1882. 

2.  Bateson.  "On  Numerical  Variation  in  Teeth,  with  a  Discussion  of  the  Conception  of 
Homology,"  Proc.  Zool.  Soc,  1892. 

3.  Baume.    "Odont.  Forschungen,"  i  Theil.    Versucheiner  Entwicklungsgesch.  d.  Gebisses,  1882. 

4.  Berten.     Correspondenz-Blatt  fiir  Zahnarzte,  1910. 
g.  Concise  Knowledge  Library.    Natural  History,  1897. 

6.  Edwards,  H.  H.    "The  Missing  Incisors  in  Man,"  Joiirn.  Brit.  Dent.  Assoc,  1885. 

7.  Flower.  "Remarks  on  the  Homologies  and  Notation  of  the  Teeth  of  the  Mammalia,  "  Journ. 
of  Anatomy  and  Physiology,  1869,  vol.  iii. 

8.  Giinther.    "An  Introduction  to  the  Study  of  Fishes,"  1880. 

9.  Johnston,  Sir  Harry.     "British  Mammals,"  The  Wobum  Library,  1903. 

10.  Rosenberg.  "Ueber  Umformungen  an  den  Incisiven  der  zweiten  Zahngeneration  des 
Menschen,"  Morphotog.  Jahrbuch,  1895. 

11.  Schmeil.    "A  Text-book  of  Zoology,  "  1908. 

12.  Sclater,  W.  L.  and  P.  L.    "The  Geography  of  Mammals,"  1899. 

13.  De  Terra.    "  Beitrage  zur  einer  Odontographie  der  Menschenrassen,  "  1905. 

14.  Turner.  Sir  Wm.     "Journal  of  Anatomy  and  Physiology,"  1885,  vol.  xix. 

15.  Tomes,  C.  S.    "A  Manual  of  Dental  Anatomy,"  1904. 

16.  Wilson,  A.     Journ.  Brit.  Dent.  Assoc,  1885. 

17.  Windle  and  Humphreys.    "Man's  Lost  Incisors,"  Journ.  Anatomy,  1886,  vol.  xxi. 


CHAPTER    IV 
THE    MORPHOLOGY    OF   THE   TEETH 

General  Considerations  Regarding  the  Shapes  of  Teeth. — Examples  in  Fishes,  Reptiles,  and  Mam- 
mals.— Definitions  of  Individual  Teeth. — Reasons  for  Morphological  Variations. — Adaptive 
Modification  as  Exemplified  in  Trigla  and  Lophius  Piscaiorius,  in  Viperine  Snakes,  in  Mar- 
supials.— Definitions  of  Types  of  Collective  Dentitions. 


THE    FORMS    OF    TEETH 

The  next  consideration  in  connexion  with  this  study  is  concerned 
with  the  shapes  of  the  crowns  of  the  teeth.  The  fishes  offer  very  many 
different  examples;  the  reptiles  and  the  mammals  less.  In  all,  however, 
these  shapes  appear  to  be  dependent  upon  the  morphological  modifi- 
cations of  (i)  a  cone,  (2)  a  flat  plate,  (3)  a  prism,  (4)  a  cylinder,  and 
(5)  a  blade  or  leaf.^ 

In  Fishes. — Examples  of  all  these  changes  of  shape  are  seen  in  fishes. 
Conical  teeth  may  be  slender,  like  a  thin  rod;  sharp;  pointed;  short; 
very  numerous;  closely  set  side  by  side,  as  the  debits  en  velours  in  the 
perch;  equally  fine  and  numerous,  but  longer  and  stronger,  as  the 
dents  en  brasses,  found  in  the  Chaetodonts;  still  larger  in  size,  as  the 
dents  en  cardes  of  the  Silurus,  or  catfish,  which,  next  to  the  "surgeon- 
fish,"  is.  the  largest  of  all  fresh-water  European  fishes,  and  possesses 
on  its  Palatine  bones  teeth  of  all  three  denominations.  In  the  Platax, 
a  species  of  chsetcdont,  called  the  sea-bat,  this  cone  is  triplicated 
at  its  cutting  extremity  and  becomes  shaped  like  a  trident.  If  the 
base  of  the  cone  is  thickened,  then  the  result  is  conical,  similar  to  the 
pattern  of  the  teeth  of  the  pike.  A  short,  pointed  tooth  is  found  in 
the  wolf-fish  {Anarrhichas  lupits)  at  the  front  of  the  mouth.  If  the 
apex  of  this  tooth  is  flattened,  shortened,  expanded,  and  thus  made 
blunter,  a  cylindrical  or  hemispherical  form  ensues,  as  shown  by  the 
posterior  teeth  of  the  Anarrhichas  lupus  or  the  posterior  teeth  of 
the  Sargus  (sheep's-head  fish)  (Fig.  51).      It  is  clear  that  these  fishes 


THE  FORMS  OF   TEETH 


85 


use  these  teeth  for  different  purposes;  the  cone-shaped  teeth  in  the 
front  of  the  mouth  for  phicking  shell-fish,  such  as  limpets,  from  off 
the  rocks,  and  the  posterior  teeth  for  crushing  the  shells  before  extract- 
ing the  contents.  If  these  posterior  teeth  are  made  still  flatter,  the 
mouth  exhibits  on  the  Pharyngeal  bones  the  effect;  and  if  still  further 
flattened,  until  the  posterior  teeth  become  greatly  increased  in  the 
transverse  and  not  in  the  vertical  diameter,  there  result  the  oblong 
or  square  plates,  as  seen  in  the  extinct  Placodus.  In  this  way  the 
cone  becomes  transformed  into  the  plate  through  the  cylinder. 


Fig.  51 


Fig.  52 


Jaws  of  Sargus,  widely  distended  to 
show  the  incisiform  front  teeth,  and 
many  flat,  round  teeth  used  for  crushing 
shell-fish.      X  i. 


Jaws  of  a  globe-fish  {Tel radon).      X 


Plates  may  be  set  horizontally,  as  just  seen,  or  vertically,  as  on 
the  Pharyngeal  bones  of  the  Scariis,  or  Pseiido-scanis.  and  the  beaks 
of  the  Diodon,  or  Tetradon  (Fig.  52).  Or  they  may  be  extremely 
numerous  and  flat,  and  form  a  sort  of  tessellated  pavement,  as  in 
Myliobatis  (the  eagle-ray),  in  which  they  assume  a  hexagonal  or  pen- 
tagonal shape. 


8G 


THE  MORPHOLOGY  OF   THE   TEETH 


An  example  of  the  modification  of  the  prism  may  be  mentioned 
in  the  three-sided  teeth  of  Myliobatis,  a  carnivorous  fresh-water  fish, 


Fig. 


Jaws  of  a  Lamna  {Carcharodon) ,  a  carnivorous  shark.     X  yV-     The  jaws  are  widely  distended. 


Fig.  54 


Jaws  of  the  blue  shark  {Carcharias),  showing  the  arrangement  and  shapes  of  the  teeth.      X  i- 
The  innermost  are  the  oldest  and  about  to  be  shed. 


of  Africa  and  tropical  America;  in  the  four-sided  teeth  of  the  Scams 
and,  finally,  in  the  six-sided  teeth  of  the  Myliobatis. 

As  examples  of  modifications  of  the  cylinder  may  be  mentioned, 


THE  FORMS  OF   TEETH 


87 


also,  the  anterior  teeth  of  the  Sargiis  and  flounder,  which  have  chisel- 
shaped,  incisiform  teeth. 

Fig.  55 


Skull  of  the  carnivorous  and  predatory  hair-tail  (Trichiunis).      X  -}. 

Blade-shaped  teeth  are  very  common  in  fishes;  thus,  the  simplest  is 
like  a  lancet,  as  in  the  Barricuda  pike.  If  short,  small  cusps  appear, 
the  outline  is  a  little  more  complicated,  a  fact  well  exemplified  in 
Lamna  (a  shark)  (Fig.  53) ;  while  the  edges  of  the  teeth  of  Carcharias 

Fig.  56 


Skull  of  a  crocodile  {Crocodilus  americanus).      X  to- 

(Fig.  54)  are  quite  serrated.  The  higher  modification  of  the  blade 
pattern,  which  resembles  very  closely  a  surgeon's  notched  lancet,  is 
found    in    Trichiunis   (Fig.    55),    called    the    "hair-tail,"    and    in   the 


88  THE  MORPHOLOGY  OF   THE   TEETH 

Acanthurus,  or  surgeon-fish.  These  latter  are  found  in  tropical  seas. 
They  feed  on  corals  and  vegetables,  having  on  each  side  of  their  tails  a 
spine  like  a  surgeon's  lancet,  capable  of  inflicting  a  severe  wound. 

In  Reptiles. — These  are,  as  a  general  rule,  simple  cones,  with  curved 
crown  and  sharp  apex.  They  are  usually  oval  in  transverse  section, 
thick  and  round  in  the  crocodile  (Fig.  56),  round  and  very  sharp,  as 
in  the  snake.  In  the  iguana  they  are  slender,  having  lobed  or  serrated 
apices. 

In  Mammals. — Simple  cones  are  found,  pointed  and  curved,  as  in 
the  dolphin.  This  homodont  dentition  does  not  represent  a  primitive 
pattern,  but  a  degeneration  or  retrogression  from  the  typical  carniv- 
orous type.       Simple  flattened   cones  are   seen  in  the  mouths  of   the 

Fig-  57 


Skull  of  an  armadillo.      X  |. 

armadillo  (Fig.  57),  the  three-toed  sloth  (Fig.  58),  and  the  Cape  ant- 
eater  (Aard-vark)  (Fig.  59).  In  the  two-toed  sloth  (Fig.  318)  the  two 
tusk-like  anterior  teeth  are  larger  than  the  rest,  for  piercing  and  tearing 
purposes.  In  nearly  all  other  orders  of  the  Mammals,  specialized 
forms  are  for  special  purposes.^  The  cone-shaped  teeth  in  mammals, 
which  are  so  well  seen  in  the  mouth  of  the  dolphin,  correspond  to  the 
tusks  (incisors)  of  the  elephant,  and  the  canines  of  the  walrus  and  the 
wild  boar;  and  they  are  designated  "chisel  teeth"  when  applied  to 
the  incisors  of  the  rcdents. 

The  highest  degrees  of  complexity  in  shape  in  mammals  are  the 
blade-like   "carnassials"   of  the   cat  or   tiger   (Fig.    67).      The   fourth 


THE  FORMS  OF   TEETH 

Fig.  58 


89 


Jaws  of  the  three-toed  sloth  {Bradypus  Iridaclylus)  placed  side  by  side  to  show  their  relative 
shapes,  lengths,  and  widths.  X  f.  There  are  five  pairs  of  simple  cheek  teeth  in  the  upper  and 
four  pairs  in  the  lower  jaw.     Cf.  Fig.  319. 


Fig.  59 


WT 


Jaws  of  Aard-vark  {Orycteropus  capensis).  X  \.  There  are  tour  pairs  of  cheek  teeth  present. 
They  possess  no  enamel  and  are  composed  of  plici-dentine — a  unique  feature  in  the  mammalia. 
The  jaws  are  placed  side  by  side  to  show  their  relative  shapes,  lengths,  and  widths. 


90 


THE  MORPHOLOGY  OF  THE  TEETH 


premolar  is  the  "carnassial"  in  the  maxilla,  the  first  molar  is  the 
"carnassial"  in  the  mandible;  they  vary  very  remarkably  in  shape 
and  in  size,  as  will  be  seen  later  on.  The  lower  carnassial  in  the  tiger, 
lion,  and  cat  differs  from  that  of  the  dog  in  the  fact  that  it  is  blade- 
like, and  has  no  tubercle  or  heel.  A  cat  does  not  masticate  its  food, 
but  a  dog  does,  especially  of  a  soft  consistency. 


Jaws  of  the  Antarctic  leopard  seal  {Stenorhynchus) .      X  J. 

Secondly,  another  degree  of  complexity  in  pattern  is  seen  in  the 
notched  teeth  of  the  seal,  thus  formed  for  the  prehension  of  slippery, 
living  prey,  like  fish.  This  is  shown  especially  well  in  the  leopard  seal 
(Fig.  60). 

Thirdly,  the  molars  of  the  elephant  and  horse  are  composed  of 
irregular  plates  of  dentine  and  enamel,  held  together  by  cementum 
(Fig.  61). 

Fourthly,  the  pectiniform  teeth  of  the  Galeopithecus — for  the  purpose 
of  combing  its  fur.  And  lastly,  the  ptychodont  dentitions  of  hares 
and  rabbits  afford  further  examples  of  diversity  in  form  of  crown. 


THE  FORMS  OF   TEETH 


91 


A  cin!4ulum  is  found  in  some  of  the  Carnivora,  and  is  well  developed 
in  animals  like  the  hysena  (Fig.  62),  as  well  as  in  insectivorous  types 
of  teeth.  It  is  an  enlargement  of  the  cervical  parts  of  the  teeth,  and 
its  function  is  to  protect  the  gum  margin  from  injury  by  splinters  of 
bone  or  hard  substances.  The  food  of  the  hyaena  is  generally  dead 
animals  and  carrion,  and  by  means  of  its  dental  cingula  it  is  enabled 
to  crunch  up  bones  without  doing  any  harm  to  the  gums  and  root 
membranes  of  the  teeth. 


Coronal  aspect  of  molars  of  (^4)  African  and  (5)  Indian  elephant.      X  4. 


It  is  probably  the  absence  of  the  cingula  in  the  premolars  and  molars 
■of  the  horse  which  accounts  for  the  prevalence  of  certain  forms  of 
•dental  periostitis  which  is  common  when  this  animal  is  in  a  domesti- 
cated state,  for  small  pieces  of  chopped  hay,  blades  of  grass,  stalks  of 
corn,  etc.,  can  easily  penetrate  the  gum  margins  of  these  cheek  teeth. 

Definitions. — It  is  now  necessary  to  distinguish  between  the  various 
kinds  of  teeth  found  in  the  mouth  of  Man  and  Mammals  generally. 
The  following  definitions  supply  the  present  needs  of  the  reader: 


92 


THE  MORPHOLOGY  OF  THE  TEETH 


The  upper  Incisors  are  teeth  implanted  on  the  Premaxillary  bone ;  the 
lower  incisors  are,  in  occlusion,  the  corresponding  teeth. 

The  upper  Canine  is  that  tooth  implanted  in  the  maxillary  bone, 
which  is  placed  immediately  behind  the  premaxillary  suture.  The 
lower  canine  is  the  tooth  in  the  Mandible  which  closes  in  front  of  the 
upper.  In  animals  such  as  the  ox,  the  giraffe,  etc.,  where  there  are 
no  maxillary  incisors  or  canines  which  could  be  used  as  a  guide,  the 
fourth    tooth    from  the    symphysis  of    the   Mandible   is   the    canine, 


Skull  of  a  hysna. 


X  |.      Cf.  Fig.  260.     The  first  right  maxillary  premolar  is  missing  and  the 
first  maxillary  molars  are  invisible  in  this  photograph. 


although  it  may  closely  resemble  an  incisor.  It  is  a  canine  because 
it  erupts  much  later  than  the  other  three,  and  because  mammals  have 
no  fourth  incisor  except  the  polyprotodont  marsupials. 

The  Premolars  are  those  teeth  in  front  of  the  molars  which,  in 
typical  diphyodonts,  replace  deciduous  predecessors. 

The  permanent  Molars  are  teeth  at  the  back  of  the  mouth  which 
erupt  behind  the  "milk"  teeth  and  have  no  predecessors.  The  decidu- 
ous molars  are  those  which  are  replaced  by  the  premolars. 


REASONS  FOR  MORPHOLOGICAL   VARIATIONS  93 


REASONS    FOR    MORPHOLOGICAL    VARIATIONS 

Having  already  seen  how  diversified  are  the  shapes  of  the  teeth, 
the  next  consideration  must  be:  "What  has  brought  about  these 
variations  in  dental  shape  and  pattern?"  It  is  difficult  to  answer 
this  question  very  satisfactorily.  At  all  events,  two  theories  may  be 
mentioned,  which  perhaps  throw  some  light  upon  the  question. 

Inheritance. — Inheritance,  or  following  an  original  pattern  or 
model,  or  type,  was  for  many  years  the  accepted  theory  as  to  the 
cause  of  these  morphological  variations.  This  was  known  for  genera- 
tions as  the  Archetype  Theory.^ 

Adaptive  Modification. — But  there  is  a  newer,  and  more  scientific  ex- 
planation in  connection  with  the  matter,  viz.,  that  certain  progressive, 
slow  modifications  from  few  and  simple  forms,  in  which  disused  organs 
deteriorate  and  much  used  organs  develop,  have  produced,  in  the 
course  of  ages,  these  mutations  in  shape.  This  theory  of  i\daptive 
Modification  of  organs  is  probably  correct.  As  an  example  of  dis- 
used organs  degenerating,  in  addition  to  those  before  mentioned,  it  is 
interesting  to  note  that  the  rudimentary  condition  of  the  eyes  of  the 
Amblyopsis — a  bony  fish  found  in  the  water  in  the  depths  of  certain 
caves  in  Kentucky — is  probably  produced  by  the  darkness  of  their 
subterranean  dwellings.  The  intense  lack  of  light  in  these  huge  caves 
is  of  no  use  to  these  fishes  for  the  purposes  of  getting  their  food.  Their 
eyes  are  not  wanted  for  visual  purposes,  and  they  have,  in  the  course 
of  evolution,  degenerated. 

It  has  been  shown  experimentally  that  it  is  possible  to  create  arti- 
ficially this  loss  of  sight.  Professor  Thomson,  the  Regius  Professor 
of  Natural  History  in  the  University  of  Aberdeen,  draws  attention, 
in  "Knowledge,"  1912,  to  some  observations  made  by  Mr.  Ogneff 
in  this  direction.  Goldfish  were  kept  in  absolute  darkness  for  a  period 
of  over  three  years,  in  aquaria  with  an  abundance  of  food.  The  struc- 
ture of  the  pigment  epithelium  of  the  eyes  became  completely  altered, 
and  the  rods  and  cones  of  the  retina'  disappeared.  The  fish  became 
totally  blind.  Other  pigment  and  structural  alterations  simultane- 
ously occurred.      At  the  end  of  the  first  twelve  months  the  fish  had 


94 


THE  MORPHOLOGY  OF   THE   TEETH 


Fig.  63 


become  black;  but  after  the  second  year  they  assumed  their  golden 
appearance  again,  the  reasons  apparently  being  that  the  black  color- 
matter  was  produced  by  the  superficial  extension  of  dark  pigment 
cells,  which  were,  in  time,  absorbed  by  certain  phagocytes,  resulting 
in  the  re-exposure  of  the  golden  cells  of  the  deeper  layer. 

Certain  deep-sea  fish  in  the  Indian  Ocean  are  blind,  or  nearly  so. 
To  compensate  for  the  dimness  of  the  sense  of  sight,  many  have  curious 
and  interesting  antennae  largely  developed  on  their  heads  for  tactile 
purposes,  thus  assisting  in  the  capture  of  their  prey.      It  has  already 

been  shown  that  the  Gangetic  dol- 
phin, which  is  practically  blind,  has 
an  enormous  number  of  teeth. 

Examples  of  Adaptive  Modi- 
fication. —  Certain  examples  of 
Adaptive  Modification  of  individual 
organs  may  be  noted:  The  Trigla 
(Fig.  63),  a  gurnard  (the  rouget  of 
the  French),  has  the  anterior  portion 
of  its  pectoral  fins  adaptively  modi- 
fied into  three  jointless  tentacles, 
which  serve  the  purposes  of  loco- 
motion. By  means  of  these  ray-like 
appendages  the  fish  is  enabled  not 
only  to  walk  on  the  surface  of  the 
floor  of  the  sea,  but  also  to  use  them  as  tactile  organs,  in  the  same  way 
as  the  antennae  in  the  deep-sea  fish  in  the  Indian  Ocean.  According 
to  Giinther,^  this  sense  of  touch  in  the  tentacles  of  the  Trigla  is 
very  highly  developed,  the  medulla  oblongata  being  specially  bulbous 
to  provide  an  efficient  nervous  mechanism  for  the  control  of  the 
tactile  sense. 

Another  excellent  example  of  adaptive  modification  of  fins  is  seen 
in  the  angler  fish,  or  Lophiiis  piscatorius.  This  fish  lives  in  the  mud, 
a  lazy  life.  The  anterior  portion  of  the  dorsal  spine  has  been  con- 
verted into  a  long,  stiff,  bristle-like  tentacle,  somewhat  like  the  end 
of  a  fishing  rod.  This  similitude  is  heightened  also  by  its  position,  at 
the  extremity,   of  a  little  bushy  mass,   which  closely  resembles  the 


A  Trigla,  showing  at  A  the  three  jointless 
limbs  of  the  anterior  portions  of  the  pectoral 
fins.      X  h. 


REASONS  FOR  MORPHOLOGICAL  VARIATIONS 


95 


bait  of  a  fisherman.  The  fish  Ues  in  wait  for  its  prey,  which,  swimming 
overhead,  sees  an  imaginary  bait  at  the  end  of  a  fishing  rod.  On 
grasping  it,  the  huge  mouth  of  the  sea-angler  is  opened,  and  the  prey 
is  easily  engulfed.^ 

But  perhaps  even  more  striking  still  are  the  variations  of  the  teeth 
of  snakes.  The  python  (Fig.  64),  which  is  a  harmless  snake — that  is 
to  say,  does  not  kill  its  prey  by  poison,  but  by  compression  in  the 
coils  of  its  body — has  two  upper  rows  of  teeth — an  outer,  on  the 
Premaxillary  and  Maxillary  bones,  and  an  inner,  on  the  Palatine  and 
Pterygoid  bones.  It  has,  also,  of  course,  teeth  on  the  mandible. 
The  vipers,  on  the  other  hand,  represent  the  class  of  poisonous 
snakes.      They   have    enormously    developed    poison    fangs,    the    rest 


Fig.  64 


I    ;i    li\llli.ll.        X    f. 


of  the  maxillary  teeth  being  lost,  or  nearly  lost,  and  the  bones  of  the 
skull  at  the  same  time  greatly  shortened  in  the  antero-posterior  direc- 
tion. The  vipers  kill  their  prey  by  injecting  poison  into  their  bodies. 
Intermediate  between  the  pythons  and  the  vipers  are  naturally  placed 
the  Colubrines,  which  are  classified  as  Aglypha,  which  are  harmless, 
and  have  no  notched  teeth — exemplified  in  the  common  English 
snake;  secondly,  the  Opisthoglypha  colubrines,  where  the  back  teeth 
are  grooved  and  not  very  poisonous;  and,  finally,  the  Proteroglypha 
colubrines,  where  ever}-  one  is  a  poisonous  snake.  The  solid  teeth 
are  reduced  in  number,  those  on  the  Maxillary  bone  are  diminished, 
and  the  front  teeth,  considerably  longer  and  larger  than  those  behind, 
having    become    grooved,  are  used    as   poison    fangs.       Thus,    in  the 


96  THE  MORPHOLOGY  OF   THE   TEETH 

evolution  of  the  poison  fangs  of  snakes,  and  as  the  result  of  the 
adaptive  modification  of  organs  collectively,  are  found  examples  of 
open-grooved  poison  fangs,  close-grooved  poison  fangs,  and  complete 
poison  fangs. 

The  method  of  erection  of  the  poison  fang  in  the  viperine  snakes 
is  as  follows:  The  digastric  muscle,  on  contraction,  draws  up  the 
Mandible,  which,  acting  on  the  lower  end  of  the  Quadrate  bone,  pushes 
it  in  a  forward  direction.  This  bone,  articulating  with  the  Pterygoid 
and  Palatine,  which  are  similarly  pushed  forward,  tilts  the  Trans- 
verse bone  from  a  horizontal  into  a  vertical  position,  and  at  the  same 
time,  with  its  articulation  of  the  Maxillary  bone,  causes  the  latter  to 

Fig.  65 


Poison  fangs  of  a  viper,  with  a  bristle  passing  tlirough  one  of  the  canals.     X  x- 

move  downwards  and  forwards,  instead  of  backwards,  as  in  the  closed 
condition  of  the  mouth.  The  poison  fang,  being  attached  securely 
to  the  Maxillary  bone,  instead  of  lying  flat  on  the  palate,  now  assumes 
a  vertical  position.  The  whole  of  the  method  of  the  erection  of  the 
poison  fang  is  a  beautiful  adaptation  by  Nature  to  prevent  the  loss 
of  this  important  organ  amongst  the  poisonous  snakes  (Fig.  65). 

Finally,  another  example  of  adaptive  modification  of  collective 
organs  may  be  found  in  the  dentition  of  the  kangaroo  (Fig.  66).  It 
has  been  discovered  in  this,  and  in  other  marsupial  animals,  that  the 
imperfect  foetuses  are  not  expelled  from  the  uterus,  as  in  placental 
mammals,  because  the  whole  group  of  animals  inhabiting  the  Australian 


REASOXS  FOR  MORPHOLOGICAL    VARIATIONS  97 

continent,  apart  from  those  artificially  introduced  by  Man,  are  impla- 
cental,  that  is,  they  do  not  possess  placentae.  But  the  nude  larvae  pass 
through  a  tube  from  the  uterus  to  the  maternal  pouch,  where  they  get 
attached,  as  shapeless  masses,  no  bigger  than  the  thumb,  to  the  mam- 
mary teats  in  the  pouch.  Here  they  remain  a  long  time,  their  nourish- 
ment being  provided  by  the  contraction  of  the  abdominal  muscles  upon 
the  breasts,  which  action  supplies  abundant  milk  diet.  Nature  has 
arranged  a  modification  in  the  conformation  of  the  oral  and  nasal 
cavities,  so  that  the  act  of  feeding  the  young  will  not  stifle  them,  by 
preventing  them  from  breathing.  Thus  the  marsupial  animals  do  not 
require  an^'  teeth  while  they  are  in  the  young  condition. 


Skull  of  the  kangaroo  {Macropus  nifiis) 


Have  kangaroos  any  milk  teeth?  Probably  not,  because  they  are 
not  wanted.  A  German  writer,  Leche,-*  found  some  rudimentary 
calcified  teeth  in  sections  which  he  made  of  the  jaws  on  the  labial  side 
of  the  functional  tooth  germs;  but  two  Australian  observers — Wilson 
and  Hill" — believe  that  these  germs  are  those  of  ordinary  milk  teeth, 
which  have  been  suppressed  because  of  disuse.  Dr.  jMarett  Tims 
considers  that  the  upper  first  premolar,  which  apparently  is  lost  early 
in  the  marsupials  and  is  the  only  tooth  which  might  perhaps  be  called 
a  deciduous  tooth,  is  probably  not  a  milk  tooth  at  all,  but  belongs 
to  the  same  dental  series  which  persists  throughout  the  life  of  the 
animal.  Recent  examinations  of  specimens  confirm  this  view.'  Its 
situation  above  the  first  molar  in  the  upper  jaw  is  probably  due  to  the 

7 


98  THE  MORPHOLOGY  OF   THE   TEETH 

kinking  or  folding  of  the  tooth  band  in  the  foetal  state.  Thus  it  is 
probable  that  in  the  jaws  of  these  animals  the  dentitions  have  become 
adaptively  modified  to  the  requirements  of  the  creatures  generally, 
and  further  that  they  exist  in  the  most  diversified  forms,  adapted  to 
different  modes  of  life. 

As  living  depends  upon  eating,  and  eating  depends  upon  the  efficiency 
of  the  teeth,  it  is  not  surprising  to  learn  that  all  kinds  of  dentitions  are 
found  amongst  the  marsupial  animals. 

There  are  examples  of  the  carnivorous  type  in  the  thylacines,  whose 
dental  formula  is  If  C  t  Pm  I  M  f;  the  herbivorous  type,  as  in 
the  kangaroo,  in  which  the  formula  is  I  f  C  ^  Pm  I  M  f ;  the  insec- 
tivorous type,  as  seen  in  the  Myrmecobius,  in  which  the  formula 
is  If  C  T  Pm  I  M  |.  There  are  also  rodent-like  marsupials,  as 
exemplified  in  the  wombat,  in  Avhich  the  formula  is  I  y  C  |  Pm  y  M  f; 
honey-eaters  as  the  tarsipes  and  the  arboreal  leaf- feeder,  the  Koala. 


TYPES    OF    DENTITIONS 

Definitions. — The  distinguishing  characteristics  of  these  different 
types  of  dentition  must  now  be  noticed. 

Carnivorous,  i.  e.,  flesh-feeders,  (i)  There  are  six  incisors  in  a 
straight  line — rather  small  teeth.  These  are  used  for  scraping  the 
muscles  and  their  attachments  off  bones.  (2)  The  canines  are  large 
and  very  prominent;  they  are  used  for  wounding  prey  or  seizing  it, 
and  for  other  prehensile  purposes.  (3)  The  premolars  are  like  blades, 
small  in  front,  and  very  much  larger  behind.  They  are  used  for  sec- 
torial purposes,  very  much  in  the  same  way  as  scissors.  (4)  Carnassials 
are  present,  namely,  the  upper  fourth  premolar  and  the  first  lower 
molar.  (5)  The  molars  are  small  in  size  and  reduced  in  number.  In 
the  FelidcB,  for  instance,  which  are  typical  carnivorous  animals,  the 
molar  is  a  tiny  mound  placed  behind  and  to  the  inside  of  the  posterior 
surface  of  the  huge  fourth  premolar.  The  lower  permanent  molar, 
however,  is  a  large  tooth,  and  to  the  casual  observer  appears  as  if  it 
were  a  premolar.  It  is  not  a  premolar,  however,  because  of  its  develop- 
ment.    It  has  never  had  a  deciduous  predecessor,  and  it  has  erupted 


TYPES  OF  DENTITIONS  99 

behind  the  other  premolars.  The  upper  molar  in  the  Felida  is  prob- 
ably functionless,  but  it  is  believed  that  the  dog  uses  it  for  chewing 
leaves  of  grass.  (6)  There  is  a  broad  short  dental  arch.  (7)  The 
temporo-mandibular  articulation  exhibits  a  true  example  of  a  ginglymus 
or  hinged  joint,  the  condyle  being  transverse  (Fig.  67). 

Fig.  67 


The  carnivorous  type  of  dentition.      X  \-     Skull  of  a  lion   (Felts  leo). 

Herbivorous,  i.  e.,  vegetable-eaters,  (i)  There  are  few  incisors;  the 
rule  is  that  there  are  no  maxillary  incisors,  their  place  being  occupied  by 
a  thick  pad  of  gum.  (2)  The  canines  are  rudimentary  or  absent,  unless 
they  are  used,  as  has  already  been  pointed  out,  as  sexual  weapons, 
as  in  the  wild  boar  and  in  the  musk  deer.  (3)  The  premolars  are  well 
developed;  usually  about  three  or  four  in  number.  (4)  There  are  no 
carnassials.  (5)  The  molars  are  large  in  size  and  normal  in  number. 
They  are  hypsodont,  that  is,  possess  tall  crowns.  This  is  true  in 
some  classes  of  herbivorous  animals,  namely,  those  which  graze,  like 
the  antelope,  the  sheep,  the  ox,  etc.,  which  eat  grass  and  corn.  Here 
it  is  obvious  that  strong,  tall  teeth  will  be  necessary  to  stand  the 
wear  and  tear  on  account  of  the  nature  of  their  food.  But  the  other 
herbivorous  animals,  like  the  giraffe,  for  instance,  which  merely  browse, 
and  do  not  require  to  do  such  hard  work  of  mastication  as  grass  requires, 
have  simply  blunt  (bunodont)  cheek  teeth.     Sheep  eat  grass  and  corn, 


100 


THE  MORPHOLOGY  OF   THE   TEETH 


deer  eat  grass  and  leaves — they  graze;  the  giraffe  browses,  eating 
leaves  only.  It  uses  its  lower  incisors  for  twisting  off  from  the  tree  or 
from  the  ground  the  leaves  and  grass  on  which  it  feeds.  (6)  There  is 
a  long,  narrow  dental  arch.  (7)  The  condyle  is  globular,  which  allows 
of  free  lateral  movements  of  the  mandible  (Fig.  68). 


The  herbivorous  type  of  dentition.    Skull  of  a  hornless  sheep.     X  5.    The  external  alveolar  plates  have 
been  removed  to  show  the  sizes,  shapes,  and  positions  of  the  roots  of  the  selenodont  teeth. 


The  insectivorous  type  of  dentition.      X  x- 

Insectivorous,  i.  e.,  insect-eaters,  (i)  There  are  not  less  than  two 
pairs  of  incisors  in  the  mandible,  of  which  the  first  pair  is  often  larger 
than  the  others.  They  are  not  chisel-shaped.  (2)  The  canines  generally 
are  not  larger  than  the  other  teeth,  except  in  the  mole.  (3)  The  pre- 
molars have  many  cusps.     (4)  The  molars  have  many  sharp  cusps  either 


TYPES  OF  DEN Tir IONS  101 

arranged  in  the  form  of  a  V  or  of  a  W,  to  enable  the  possessor  to  crunch 
up  the  chitinous  envelopes  of  the  bodies  of  their  prey.  (5)  The  skulls 
are  small  in  size  (Fig.  69). 

Fk;.  7" 


Lmgual  aspects  of  the  jaws  of  an  adult  man,  showing  the  normal  arrangement  of  the  permanent 
teeth  in  the  dental  arches.  X  |.  An  example  of  a  typical  omnivorous  dentition.  The  premolars 
are,  clinically,  the  first  and  second,  but,  anatomically,  they  are  the  third  and  fourth  of  the  typical 
mammahan  dentition. 


102  THE  MORPHOLOGY  OF   THE   TEETH 

As  an  example  of  mixed  type  of  dentition  Man  is 

Omnivorous  (Fig.  70).  The  pig  also  is  omnivorous.  In  the  pig 
and  the  wild  boar  the  canines  are  large  and  powerful,  for  digging 
up  roots;  the  lower  incisors  are  procumbent,  that  is,  placed  in  a  hori- 
zontal instead  of  a  vertical  position,  for  grubbing  in  the  ground.  The 
anterior  cheek  teeth  are  used  for  breaking  up  and  dividing  into  pieces 
the  food,  while  the  molars  crush  it  and  masticate  it;  but  as  mastica- 
tion of  matter  is  not  so  essential  in  pigs  as  in  the  ruminants  and  other 
grass  and  leaf-eating  animals,  the  molars  in  the  pigs  have  low,  blunt 
(brachyodont)  crowns.^ 

Thus,  in  conclusion,  we  find  that  the  cone  and  its  modifications 
are  used,  amongst  other  purposes,  for  combat,  for  seizing  prey,  or 
killing  it  by  injection  of  poison;  the  cylinder  and  its  modifications  for 
combat;  the  prism  or  plate  for  crushing  food;  and  the  blade-shaped 
tooth  for  tearing  or  cutting  up  food  into  small  pieces;  and  that  animals' 
teeth  have  been,  in  the  course  of  evolution,  adaptively  modified  to 
serve  these  different  functions. 

Referenxes 

1.  Flower  and  Lydekker.    "Mammals,  Living  and  Extinct,"  1891. 

2.  Giinther.    "The  Study  of  Fishes,  "  1880. 

3.  Hopewell-Smith  and  Marett  Tims.     "Tooth  Germs  in  the  Wallaby  Macropus  Billardieri," 
Proc.  Zoolog.  Soc,  London,  1911. 

4.  Leche.     "Zur  Entwicklungsgeschichte  des  Zahnsystems  der  Sdiigetiere,  zugleich  ein  Beitrag 
zur  Stammesgeschichte  dieser  Tiergruppe, "  1895. 

5.  Owen.     "Odontography,"  1840. 

6.  Tomes.    "A  Manual  of  Dental  Anatomy,"  1904. 

7.  Wilson  and  Hill.     "Observations  upon   the   Development   and   Succession   of  the  Teeth  in 
Parameles,"  Quart.  Jour.  Micro.  Sciejice,  1896. 


CHAPTER    V 


DARWINIANA 


The  Origin  of  Variations  of  Species. — History. — The  Theories  of  Linnaeus,  Cuvier,  Lamarck, 
Goethe,  Darwin. — Natural  Selection. — Sexual  Selection. — Dental  Variations. — Atypical 
Dental  Heredity. — Evidences  of  the  Mutability  of  Species. — Proofs  of  Derivation  of  Species. 
— Post-Darwinian  Theories. — The  Mutation  Theory. — Mendelism. 


ORIGIN    OF    VARIATIONS    OF    SPECIES 

Introductory. — Having  now  noted  the  differences  existing  in  several 
types  of  the  dentitions  of  animals — Insectivorous,  Carnivorous,  Her- 
bivorous, etc. — and  having  seen  that  the  Adaptive  Modification  of 
organs  plays  a  great  part  in  producing  variations  in  the  shape,  size, 
and  number  of  the  teeth,  as  evidenced  in  the  poisonous  fangs  of  snakes, 
etc.,  it  is  quite  clear  that  variations  in  animals  are  extremely  common, 
and  their  species  too  are  very  numerous.  It  is  probable,  however,  that 
all  had  a  common  origin.  A  cell  or  tiny  organism  is  capable  of  becom- 
ing an  elephant  or  a  frog,  a  crocodile  or  an  ape.  Why  is  this?  In 
other  words:  "How  have  variations  which  have  resulted  in  the  forma- 
tion of  millions  of  species  of  animals,  insects,  and  plants  arisen?"  The 
answer  is  to  be  found  in  Darwin's  works.  The  same  rules  which  apply 
to  variation  in  animals  apply  also,  more  or  less,  to  teeth,  and  it  is 
necessary,  in  order  to  understand  the  operative  forces  which  have 
produced  these  variations  of  teeth,  to  have  a  superficial  knowledge, 
at  all  events,  of  the  work  of  Charles  Darwin.  For  it  is  clear  that  there 
are  three  great  agencies,  apart  from  possible  others,  which  seem  to 
influence  the  varying  shapes  of  animals  and  their  teeth,  namely: 
(l)  a  Natural  selection  or  Survival  of  the  fittest;  (2)  Sexual  selection; 
and  (3)  Concomitant  variation  or  Correlation  of  growth,  /.  e.,  that 
obscure  agenc}'  which  affecting  one  part  or  organ  of  the  bod}'  ma>- 
secondarily  occasion  alteration  in  other  parts  or  organs  of  the  body. 

Historical. — As  a  preliminary  to  a  short  outline  of  the  Darwinian 
theory  of  evolution,  it  will  be  convenient  to  remember  the  historical 


104  DARWINIANA 

aspect  of  the  question.  It  must  be  already  predicated  that  the  subject 
is  very  vast,  and  abstruse,  and  difficult  to  crystallize  into  a  few  pages. 

In  1735  Linnaeus^^  (born  in  1707,  died  in  1778)  was  the  first  to 
classify  and  name  various  groups  of  animals  and  plants.  He  believed 
in  the  Mosaic  storj/  as  recorded  in  the  Bible,  that  is,  in  the  Creation, 
in  the  Beginning,  of  one  pair  of  each  species  of  animals  and  plants. 
But  the  science  of  palaeontology  was  unknown  to  him.  Men  had  not 
at  that  time  begun  to  find  in  the  earth  fossil  remains  of  prehistoric 
animals  and  plants. 

Cuvier,  the  great  naturalist,  at  the  beginning  of  the  Nineteenth 
Century  (i  769-1 832),  held  that,  as  the  surface  of  the  earth  revealed 
many  fossilized  bones  of  varying  size  and  character,  there  must  have 
been  several  Deluges,  and  not  one,  as  recorded  in  the  Book  of  Genesis, 
and  that  after  each  catastrophe  a  fresh  creation  of  living  things  occurred 
throughout  the  nai:ural  world.  This  was  the  Catastrophic  Theory, 
and  it  was  believed  in  for  about  fifty  years,  till  Lamarck  and  Lyell 
proved  that  the  theory  was  wrong." 

Lamarck,"  the  French  zoologist  (born  in  1744,  died  in  1829),  tried 
to  show  the  real  cause  of  the  origin  of  species,  and  was  the  first  who 
proposed  any  detailed  scientific  theory  of  the  origin  of  the  various 
species  of  organisms  by  a  natural  process  of  rriodification.  He  held  that 
there  were  no  essential  differences  between  living  and  lifeless  beings, 
Nature  being  one  united  system  of  phenomena.  Thus  he  controverted 
Cuvier's  theory.  "All  the  different  kinds  of  animals  and  plants  which 
we  see  today,"  he  wrote,  "or  that  have  ever  lived,  have  descended  in 
a  natural  way  from  earlier  and  different  species.  All  come  from  one 
common  stock  or  from  a  few  common  ancestors  of  the  lowest  type, 
arising  by  spontaneous  generation  in  organic  matter.  Succeeding 
species  have  been  constantly  modified  by  adaptation  to  their  varying 
environments  (especially  by  use  and  habit),  and  have  transmitted 
their  modifications  to  their  successors  by  heredity."'"  By  "sponta- 
neous generation,"  or  abiogenesis,  is  implied  the  theoretical  doctrine 
that  living  matter  may  be  produced  by  not  living  matter,  a  view 
supported  largely  by  Bastian,  Ponchet,  and  Haeckel.  Thus,  if  the  con- 
ditions are  favourable,  many  organisms  of  a  low  type  will  make  their 
appearance  in  infusions  of  dead  material  from  which  all  extraneous 


0 RIG IX  OF  VARIATIONS  OF  SPECIES  105 

micro-organisms  are  excluded.  The  simple  experiment  of  putting  a 
handful  of  dead  hay  into  water  proved  conclusively  to  the  minds 
of  these  earlier  investigators  the  fact  that  millions  of  bacteria  could 
and  did  become  generated,  in  due  time,  merely  from  the  presence  of 
the  hay  in  water.  No  conclusive  proof  has  been  obtained  of  the 
occurrence  of  abiogenesis.'" 

Lamarck  first  formulated  the  conclusion  that  man  descended  from 
the  ape,  explaining  this  by  applying  to  his  theory  the  testimony 
of  those  agencies  which  brought  about  the  natural  origin  of  plants 
and  animal  species.  These  agencies  are  two  in  number:  (i)  Adap- 
tation, by  means  of  use  and  habit,  and  (2)  Heredity.  Examples  of 
these  may  be  given,  as  the  long  tongue  of  the  humming-bird  and  the 
woodpecker — organs  which  were  adaptively  modified  to  serve  the 
purposes  of  these  birds.  The  neck  of  the -giraffe  and  the  web  of  the 
frog's  foot  exemplified  a  similar  principle. 

The  Lamarckian  theory  was,  in  brief,  that  every  part  or  organ  of  a 
creature  used  in  satisfying  its  wants  was  increased  in  size  or  strength 
or  otherwise  modified  by  use  and  effort,  and  that  the  modifications 
or  variations  produced  in  these  ways  were  transmitted  to  its  progeny, 
and  thus  led,  in  the  course  of  generations,  to  the  production  of  the 
various  forms  which  are  seen  everywhere  in  the  natural  world.  As 
an  example,  it  may  be  mentioned  that  the  ancestor  of  the  beaver  or 
the  frog  was  not  web-footed  in  order  that  it  might  swim,  but  its  wants 
having  attracted  it  to  a  stream  of  water  in  search  of  food,  it  extended 
the  toes  of  its  feet  in  order  to  strike  the  surface  of  the  pool  and  move 
more  rapidly  upon  it.  Thus,  in  course  of  time  were  produced  the 
broad  membranes  which  now  connect  the  toes  and  make  it  web-footed. 
Present-day  Neo-Lamarckians  (/.  c,  those  who  still  hold  the  Lamarck- 
ian views)  have  amongst  their  number  Professor  Cope,  of  America 
(see  Chapter  VIII),  whose  investigations,  however,  dealt  exclusively 
with  extinct  creatures,  and  avoided  any  attempt  to  account  for  the 
phenomena  in  living  beings. 

That  the  use  or  disuse  of  organs  was  a  very  important  factor  in 
organic  development  is  clear,  but  it  is  not  sufficient  to  explain  the 
origin  of  species.  Lamarck,  however,  failed  to  discover  the  principle 
which  Darwin  afterward  found  to  be  the  chief  agent  in  the  theory 


106  DARWINIANA 

of  transformation,  namely,  the  principle  of  Natural  Selection  in  the 
struggle  for  existence. 

Natural  Selection. — Natural  selection  may  be  defined  as:  The 
survival  of  the  fittest  in  the  struggle  for  existence;  the  agency  by  which 
variations,  beneficial  to  their  possessors,  will  be  preserved  and  intensi- 
fied in  successive  generations.  The  doctrine  underlying  the  Darwinian 
theory  is  applicable  to  the  teeth,  which  are  brought  up  to  their  highest 
state  of  efficiency,  as  exemplified,  for  instance,  in  the  incisors  of  the 
wombat  in  Australia,  the  aye-aye  in  Madagascar,  and  rodents  generally. 

But  another  man  was  the  first  forerunner  of  Darwin,  though  he 
never  formulated  evolution  as  a  scientific  system  like  Lamarck — 
Goethe,  the  great  German  poet.  In  1807  he  wrote,  in  an  "Essay  on 
the  Metamorphoses  of  Plants,"  "When  we  compare  plants  and  animals 
in  their  most  rudimentary  forms,  it  is  almost  impossible  to  distinguish 
between  them."  He  named  two  forces :  (i)  A  Centripetal  force,  which 
maintains  the  standard  of  the  specific  forms  in  the  succession  of  genera- 
tions, that  is,  heredity;  and  (2)  a  Centrifugal  force,  which  is  constantly 
modifying  species  by  changing  their  environment,  that  is,  the  adapta- 
tive  modification  of  organs. 

Then  Darwin  appeared.  He  was  born  in  1809  and  died  in  1882.  His 
successful  theory  was  based  on  a  mechanical  explanation  of  this  modi- 
fication of  plant  and  animal  structure,  by  adaptation  and  heredity. 
He  compared  the  origin  of  the  various  kinds  of  animals  and  plants 
which  are  today  modified  by  artificial  breeding  by  Man  with  the 
origin  of  the  species  of  plants  and  animals  in  their  natural  state. 

The  essentials  of  the  Darwinian  theory  are  threefold: 

I.  Man  has  made  his  domestic  breeds  of  animals  and  plants  by 
the  selection — conscious  or  unconscious — of  very  slight  or  greater 
variations. 

H.  The  material  for  selection  exists  in  Nature,  viz.,  the  slight  varia- 
tions of  all  parts  of  the  organism. 

HI.  The  "unerring  power"  which  sifts  these  variations  is  Natural 
Selection  .  .  .  which  selects  exclusively  for  the  good  of  each 
organic  being.  In  short,  in  the  struggle  for  existence  "favourable 
variations  would  tend  to  be  preserved,  and  unfavourable  ones  to  be 
destroyed.    The  result  of  this  would  be  the  formation  of  new  species." 


ORIGIX  OF  VARIATIOXS  OF  SPECIES  107 

The  struggle  for  existence  produced  new  species  without  premedita- 
tive  design  in  the  Hfe  of  Nature,  in  the  same  way  that  the  will  of  Man 
consciously  selects  new  races  under  artificial  conditions.  For  instance, 
the  horticulturist  of  today  can  produce  new  species  of  fruit  or  flower 
at  will.  It  is  possible  to  produce  a  blue  primrose  and  a  black  hya- 
cinth. The  pigeon  fancier,  the  horse  and  dog  breeder  are  able,  almost 
at  will,  to  produce  new  forms  of  bird  or  quadruped.  In  the  natural 
state  the  struggle  for  life  is  always  unconscioush*  modifying  the 
various  species  of  living  things.  This  struggle  for  life,  or  competition 
of  organisms  in  securing  the  means  of  subsistence,  acts  without  any 
conscious  design,  but  it  is  none  the  less  powerful  in  modifying 
structures.  As  heredity  and  adaptation  enter  into  the  closest  action 
under  its  influence,  new  structures  or  alterations  of  structures  are 
produced. 

This  is  the  central  thought  of  Darwinism,  but  as  yet,  Darwin  had 
no  idea  of  applying  these  principles  to  Man.  He  believed  that  Man 
held  a  special  position  in  the  universe. 

A  small  book,  entitled  "The  Evidence  as  to  Man's  Place  in  Nature," 
was  published  in  1863,  by  Thomas  Huxley.  In  it,  he  applied  to  Man 
the  Darwinian  theory,  and  eight  years  later,  Darwin's  "Descent  of 
Man"  was  printed.  The  latter  author  drew  the  conclusion  that  Man 
also  must  have  been  developed  from  lower  species,  and  he  described 
the  important  part  played  by  Sexual  selection  in  the  evolution  of 
Homo  and  the  other  higher  animals. 

Sexual  Selection. — Sexual  selection  may  be  defined  as:  The  agenc}' 
which  operates  principally  by  enabling  those  possessed  of  certain 
characteristics  to  propagate  their  race,  while  less  favoured  ones  do 
not  get  the  opportunity  of  doing  so.  For  this  end  the  males  of  some 
species  are  very  much  ornamented.  The  males  of  birds  sing;  man}' 
male  animals  possess  teeth  which  females  have  not — like  the  musk 
deer,  the  muntjac,  and  the  narwhal.  The  males  choose  the  handsomest 
females  in  one  class  of  animals,  and  the  females  choose  only  the  finest 
looking  males,  and  so  on.  These  sexual  features  are  increasingly 
accentuated.  It  is  to  this  that  we  owe  the  family  life,  which  is  the 
chief  foundation  of  civilization.  The  rise  of  the  human  race  is  largely 
due  to  the  advanced  sexual  ^selection  [which  |our  ancestors  exercised 


108 


DARWINIANA 


in  choosing  their  mates.     It  is  possible  that  sexual  selection  tends  to 
prevent  irregularities  in  the  position  of  the  human  teeth. 

Living  organisms  have  a  very  complicated  structure,  inherit  certain 
tendencies,  and  by  their  movements  and  mobility  are  capable  of  under- 
going countless  variations.  Variations  are  brought  about  by  the 
environment  of  the  organism  on  which  life  depends.  When  the  environ- 
ment of  an  animal  or  a  person  changes,  the  organism  either  adapts 
itself  to  that  change,  or  does  not  adapt  itself  to  that  change.  If  the 
former,  it  lives  and  varies  in  greater  or  less  degree;  if  the  latter,  it 
dies. 

Fig.  71 


Diagram  illustrating  "correspondence  with  environment:"  .4,  a  medusa;  i,  the  sea.  U,  an  oak; 
I,  the  earth;  2,  the  air;  3,  the  rain;  4,  the  sunshine.  C,  a  lark;  i,  the  light;  2,  the  food;  3,  music; 
4,  love  of  freedom.  D,  a  man;  i,  the  air;  2,  the  food;  3,  the  home;  4,  religion;  5,  eugenics;  6,  the 
Arabic  language,  etc. 


What  is  life?  Life  may  be  philosophically  defined  as  Complete 
correspondence  with  environment.  What  is  death?  Death  is  the 
converse  of  this,  that  is.  Incomplete  or  Imperfect  correspondence 
with  environment.  A  few  illustrations  will  make  this  clear  (Fig.  71). 
A  jelly  fish  is  alive  when  it  is  in  the  sea,  that  is,  when  it  is  in  complete 
correspondence  with  its  surroundings;  but  it  dies  when  cast  up  by  the 
sea  waves  on  to  the  shore,  because  then  its  environment  is  incomplete 
— or  it  is  in  incomplete  correspondence  with  its  environment — and 
because  it  cannot  adapt  itself  to  that  external  change.'' 

Further,  the  oak  lives  because  it  is  in  complete  correspondence 
with  its  environment,  namely,  the  ground,  the  air,  the  sky,  the  rain, 
the  sunshine;  but  let  it  be  deprived  of  one  or  more  of  these — for 
instance,  if  its  roots  are  pulled  up — it  will  die,  because  it  is  not  in 
complete  correspondence  with  its  environment. 


ORIGIN  OF   VARIATIONS  OF  SPECIES  109 

A  bird,  like  the  lark,  has  a  bigger  life  than  the  oak,  because  into  its 
short  existence  there  come  the  affections  of  home,  the  love  of  music,  the 
delight  of  freedom,  and  so  on;  and  as  long  as  it  is  in  complete  accord 
with  this  higher  environment,  it  lives.  Even  when  caged  it  may 
continue  to  exist,  because  it  is  able,  more  or  less,  to  adapt  itself  to  the 
artificial  conditions  in  which  it  finds  itself. 

Man,  too,  is  encompassed  by  numberless  forms  of  environment. 
As  long  as  he  adapts  himself  to  these,  and  is  in  perfect  correspondence 
with  them,  he  lives;  but  unless  he  is  in  perfect  correspondence  with 
them,  he  dies,  or  is  dead  to  them.  Thus,  a  knowledge  of  the  Arabic 
language  may  be  an  environment  of  a  certain  man ;  but  one  who  knows 
not  a  word  of  that  language  is  dead  to  that  environment. 

An  interesting  example  may  be  added  to  the  above.  The  common 
English  ring  snake  is  oviparous  in  its  natural  state  in  the  fields.  When 
kept  in  a  cage  in  captivity,  without  sand,  however,  it  becomes  vivip- 
arous. 

Variations  in  Teeth. — Bateson,^  during  recent  years,  has  collected 
an  enormous  amount  of  material  for  the  study  of  variation,  and  has 
very  thoroughly  investigated  the  bearing  of  it  as  it  affects  the  teeth 
of  the  vertebrates.  This  occupies  an  important  place  in  his  scheme  of 
dealing  with  a  very  abstruse  subject.  The  association  of  "diverse 
phenomena  which  are  commonly  treated  as  distinct,"  has  led  to  the 
creation  of  the  word  "Merism,"  which  means  the  phenomenon  of  the 
repetition  of  parts  generally  occurring  in  such  a  way  as  to  form  a 
symmetry  or  pattern.  This  study  of  variation  is  complicated  by  the 
occurrence  of  qualitative,  in  addition  to  simply  numerical  changes. 

The  principles  which  underlie  the  facts  would  appear  to  controvert 
the  doctrine  that  the  domestication  of  animals  induces  or  causes 
variation,  when  variation  in  wild  animals  is  taken  into  consideration; 
would  show  that  very  frequently  dental  variation  is  asymmetrical; 
that  increase  in  the  number  of  the  teeth  has  arisen  from  dichotomy 
or  division  of  a  simple  tooth  germ;  that  the  teeth  placed  at  the  ends 
of  series  are  liable  to  undergo  great  numerical  variation ;  and  that  there 
is  a  fairly  constant  relation  between  the  size  of  extra  teeth,  and  that 
of  the  teeth  next  to  which  they  stand,  so  that  the  new  ones  are,  as  it 
Avere,  from  the  first,  of  a  size  and  development  suitable  to  their  position. 


110  DARWINIANA 

In  the  man-like  apes  {SimiidcB),  Bateson  found  and  marked  numerical 
and  topographical  variations.  There  were  examples  of  supernumerary 
molars  (see  Fig.  85),  and  incisors  and  malposition  of  premolars;  in  the 
old-world  monkeys  supernumerary  incisors,  molars,  and  premolars, 
and  absence  of  molars.  In  the  carnivores  the  addition  and  absence  of 
incisors  were  noted,  dichotomy  appearing  in  a  bull-dog.  The  numbers 
of  premolars  were  increased  and  diminished,  and  in  the  molar  regions 
were  added  to.  Meristic  variability  in  the  incisors,  premolars,  and 
molars  occurred  in  cats,  wild-cats,  martens,  otters,  seals;  super- 
numerary incisors  were  observed  in  the  horse,  and  many  abnormal 
forms  in  sheep  and  marsupials.  Meristic  variation  exists  occasionally 
in  the  dentition  of  the  sharks  and  rays. 

Atypical  Dental  Heredity. — The  influences  of  heredity  are  also 
frequently  met  with  in  connexion  with  the  jaws  and  teeth.  Mr.  J. 
G.  Turner^''  has  assembled  some  cases  in  which  are  described  the  results 
of  its  operations,  producing  topographical  irregularity  of  teeth  and 
even  of  the  genesis  of  supernumerary  teeth;  and  leaving  evidences  in 
the  altered  character  of  the  jaws,  when  the  large  teeth  of  one  parent  and 
the  small  jaws  of  the  other  are  inherited.  The  Royal  family  of  the 
Hapsburgs  furnishes  a  remarkable  instance  of  hereditary  epharmosis. 

The  absence  of  teeth  and  the  endowment  of  a  conical  pattern  of 
crown — atavism — are  often  inherited.  Again,  the  acquired  peculiarities 
of  one  or  more  teeth  may  be  transmitted  to  progeny.  The  maxillary 
second  incisor  is  frequently  missing,  and  cases  have  been  recorded 
where  hereditary  reduction  in  the  numbers  of  the  teeth  and  their 
characteristics  have  been  associated  with  abnormal  conditions  of  the 
hair,  skin,  and  eyes.  Changes  in  the  structure  of  teeth,  also,  have 
been  noted.     (See  Appendix,  Note  A.) 

Thus,  the  transmission  of  variations  of  parental  form  and  structure 
to  offspring  comprises  stages  in  the  development  of  different  life  forms. 
In  short,  likenesses  are  inherited,  variations  are  acquired,  and  are, 
in  spite  of  Weissmann,  capable  of  being  transmitted  to  progeny. 
Weissmann  experimented  in  this  matter,  and  he  came  to  the  conclu- 
sion that  acquired  characteristics  cannot  be  transmitted  to  progeny. 
His  classical  experiment  consisted  of  amputating  the  tails  of  great 
numbers  of  generations  of  mice,  to  try  and  prove  that  in  the  course  of 


EVIDENCES  OF   THE  MUTABILITY  OF  SPECIES  111 

time  the  progeny  of  such  mutilated  animals  would  be  born  with  short 
tails.  He  did  not  succeed,  however.  The  probable  reason  was  that 
the  attempt  to  bring  about  the  evolution  of  the  short  tail  was  too 
sudden. 


EVIDENCES    OF    THE    MUTABILITY    OF    SPECIES 

It  is  necessary  to  add  a  summary  of  the  evidence  of  the  mutability 
of  species. - 

(i)  Every  individual  of  the  same  species,  that  is,  groups  of  individ- 
uals which  possess  characteristics  in  common,  tends  to  vary.  There 
are  no  two  people  or  individuals  exactly  alike;  there  are  no  two  people 
or  children  of  the  same  parents,  no  two  sheep,  no  two  hyacinth  bulbs, 
no  two  blades  of  grass,  no  two  finger  prints,  which  possess  identical 
characteristics.  This  tendency  to  vary  is  produced  by  changes  of 
the  environment  of  plant  or  animal;  for  instance,  the  snake,  as  just 
mentioned. 

(2)  These  variations  are  capable  of  being  transmitted  from  parent 
to  offspring;  they,  therefore,  tend  to  become  permanent. 

(3)  New  varieties  of  plants  and  animals  are  produced  by  IVIan 
artificially,  by  his  taking  advantage  of  these  transmitted  variations. 
Illustrations  may  be  given  by  mentioning  that  all  classes  of  pigeons — 
the  pouter,  the  tumbler,  the  fantail,  the  carrier,  etc. — are  derived 
from  the  blue  rock  pigeon  of  the  coasts. 

All  varieties  of  dogs — the  bulldog,  the  pug,  the  hound,  the  retriever, 
the  mastiff,  the  fox-terrier,  etc. — are  said  to  come  from  the  Indian 
wolf. 

Professor  Jeitteles,  of  Vienna,  first  suggested  this  theory  in  1877. 
It  is  concluded  that  the  dog  is  of  the  East,  coming  from  India  when 
that  country  was  undergoing  "glaciation."  The  evidence  that  the 
Indian  wolf  had  some  part  in  the  origination  of  our  dogs  is  very 
great,  but  scientists  generally  hold  that  Darwin's^  evidence  for  a  plural 
ancestry  is  overwhelminglj'  greater,  although  he  most  carefully  points 
out  that  "We  shall  probably  never  be  able  to  ascertain  their  origin 
with  certainty"  (vol.  i,  p.  17). 


112  DARWINIANA 

All  varieties  of  horses — the  race-horse,  the  cart-horse,  the  Shetland 
pony — owe  their  origin  to  the  wild-horse. 

All  the  varieties  of  apples  seen  on  a  green-grocer's  stall  claim  the 
ancestry  of  the  common  sour  crab  apple.  The  recent  experiments 
of  'Burbank,  of  America,  have  tended  to  produce  fresh  variations  in 
the  growth,  colour,  and  flavour  of  fruits  and  vegetables — potatoes, 
the  tubers  of  which  grow  above  the  ground,  fruits  possessing  the 
combinations  of  the  qualities  and  flavours  of  plums  and  apricots,  and 
so  on. 

It  was  Darwin  who  showed  that  Nature  does,  on  a  large  scale, 
during  countless  ages,  and  through  countless  generations,  what  Man 
can  do  artificially  within  a  limited  range  of  time.  This  is  Natural 
Selection. 

(4)  More  organisms  are  born  than  survive.  "There  is  no  exception 
to  the  rule  that  every  organic  being  naturally  increases  at  so  high  a 
rate  that,  if  not  destroyed,  the  earth  would  soon  be  covered  by  the 
progeny  of  a  single  pair."  If  all  the  offspring  of  a  pair  of  elephants 
that  lived  seven  hundred  and  fifty  years  ago  had  survived,  there 
would  be  today  nineteen  million  elephants  in  the  world.  One  common 
house  fly  produces  in  its  fifth  generation  at  the  end  of  eight  weeks, 
twenty-six  million  flies!  Instances  might  be  multiplied,  but  are 
unnecessary. 

(5)  The  general  conception  of  the  struggle  for  existence  is  that  the 
slightest  inferiority  in  structure  or  powers  is  sufficient  to  disqualify 
the  individual  for  survival.  From  time  to  time,  however,  facts  are 
brought  forward  tending  to  qualify  this  conception.  An  interesting 
example  is  given  by  Mr.  W.  E.  Kellicott  in  Science,  as  the  result 
of  his  study  of  an  American  species  of  toad.  Out  of  four  hundred  and 
thirty-four  individuals  examined  by  him  twenty-two  showed  injuries, 
such  as  crushed  feet,  broken  femur,  or  broken  scapula.  In  spite  of 
these  injuries,  it  did  not  appear  that  they  had  been  very  seriously 
handicapped  in  the  struggle  for  life,  for  their  average  weight  was 
38^  grains,  while  that  of  the  entire  colony  was  44^  grains.  In 
addition  to  this,  sixteen  showed  abnormalities,  some  of  which  would 
appear  to  be  serious  disadvantages  in  the  struggle  for  life.  On  the 
whole  it  is  stated    that  the  conditions  of  life  were  not  rigorous  for 


EVIDENCES  OF   THE  MUTABILITY  OF  SPECIES  113 

this   group   of   animals.      Food    was   abundant,    natural    enemies   not 
numerous,  means  of  concealment  and  protection  ready. 

Still  the  fact  remains  that  for  animals  the  struggle  for  existence 
comes  at  crises  of  their  existence.  Thousands  are  carried  off.  For  every 
species  the  struggle  may  become  a  stern  reality  at  any  time.  "Quite 
apart  from  epidemics,  it  is  probable  that  disease  kills  more  wild  animals 
than  most  people  imagine.  Even  a  small  ailment  must  be  fatal. 
Among  domestic  animals  it  is  frequent  and  visible  enough.  Even  pigs 
get  rheumatism  or  something  like  it."* 

There  is,  therefore,  usually  and  universally,  a  ceaseless  struggle 
for  food  and  place,  and  life,  which  ends  in  the  survival  of  the  fittest, 
and  this,  as  in  men  of  the  same  trade  or  profession,  is  very  severe 
between  members  of  the  same  species.  Lions  with  keener  sight  and 
greater  muscular  development  are  able  to  combat  lions  of  poorer  sight 
and  feebler  form,  and  they  survive,  while  the  weaker  ones  go  to  the 
wall.  The  man  with  quick  intellect  and  strong  physical  powers  passes 
ver}'  rapidly  the  weak  and  the  stupid  in  the  race  for  life."  It  is  quite 
unnecessary  to  point  out  that  the  subtlety,  variety,  and  complex 
character  of  the  conditions  of  animal  existence  upon  which  natural 
selection  seizes  is  amazing. 

Protective  colour  and  mimicry  play  a  very  important  part  in  the 
struggle  for  life.  The  stripes  of  the  tiger  enable  this  animal  to  roam 
about  and  pass  through  forests  of  bamboo  without  being  seen.  Coral 
fish  have  most  brilliantly  coloured  scales  on  their  bodies,  so  that  they 
may  not  be  mistaken  for  living  creatures  but  may  look  exactly  like  the 
coral  on  which  they  feed.  Flat  fish  have  a  muddy  or  gravel-like  colour 
upon  the  upper  surfaces  of  their  bodies,  in  order  that  they  will  not  be 
observed  lying  on  the  mud. 

That  some  flat  fish,  such  as  the  turbot,  are  able  not  only  to  change 
their  hues  to  conform  to  the  colour  of  the  gravel  over  which  they 
happen  to  lie,  but  to  copy  on  their  upper  surfaces  the  geometrical 
pattern  of  that  background  as  well,  has  been  observed  by  Mr.  Francis 
Sumner  in  the  United  States  Fisheries  Laboratory  at  Woods  Hole, 
Massachusetts,  in  191 1.  Biologists  have  for  many  years  believed  that 
this  alteration  in  colour  of  the  skin  was  effected  by  the  action  of  light 
upon  its  cells;  but  twenty-five  years  ago  it  was  proved  that  the  change 


114  DARWINIANA 

originated  in  the  functions  of  the  organs  of  vision.  BHnd  fish  are 
incapable  of  or,  at  least,  do  not  change  their  colour  adaptively.  A 
distinct  and  detailed  resemblance  is  noticed  between  the  skin  markings 
and  the  appearance  of  the  gravel  on  which  the  fish  lay,  and  by  means 
of  ingenious  experiments  it  was  shown  that  this  was  no  mere  coinci- 
dence, but  that  the  fish  had  the  power  of  controlling  the  colour  pattern 
as  well  as  the  general  colour  tone  of  the  body. 

A  number  of  different  backgrounds  was  prepared,  some  simulating 
various  types  of  natural  sea  bottom,  and  some  imitating  various 
unnatural  geometrical  patterns,  such  as  stripes,  screens,  checker- 
boards, etc.  After  the  fish  had  been  placed  in  the  tanks  having  one 
of  these  prepared  floorings,  it  was  found  that  it  soon  began  to  copy 
the  pattern  on  its  upper  exposed  surface.  The  time  occupied  in  this 
alteration,  ranged  from  a  few  seconds  to  several  days. 

This  imitation  of  a  geometrical  figure  is  accomplished  through  the 
flat  fish's  eyes.  The  whole  of  the  fish's  visual  field  is  not  involved  in 
the  process;  the  imitation  is  not  of  all  that  the  fish  can  see,  but  of  the 
flooring  immediately  under  or  around  it.  When  the  fish  was  blinded 
it  ceased  to  copy  the  background  pattern,  and  became  of  an  evenly 
distributed  darker  colour.  Experimenting  with  vertical  walls  of 
different  patterns  and  lines  showed  that  no  effect  was  produced  upon 
the  skin,  and  when  the  patterned  flooring  was  placed  over  the  fish 
no  change  was  noticed. 

It  has  long  been  known,  too,  that  trout  can  at  will  change  the  colour 
of  their  bodies  to  match  that  of  the  bottom  of  the  stream  which  they 
inhabit,  and  minnows  also.  All  these  instances  are  brought  about  by 
ocular  means,  and  not,  as  is  the  case  in  certain  insects,  through  the 
skin  itself,  or  general  nervous  system. 

In  the  insect  world  there  are  many  beautiful  examples  of  protective 
colouration.  The  leaf  insects  (Fig.  72),  the  butterflies,  and  moths 
show  this.  There  is  a  South  American  butterfly  whose  upper  wings 
are  coloured  blue  and  black,  while  its  under  surface  mimics  exactly 
the  face  of  an  owl.  When  it  is  pursued  by  a  bird,  all  it  has  to  do  is  to 
turn  the  under  surface  of  its  wings  to  its  pursuer,  which  flies  away  on 
sight  of  the  staring  eyes  of  the  supposititious  owl.  In  the  Zoological 
"Jahrbuch,"  1910,  Mr.  Arnold  Japha  describes  the  "  terrifying  attitude" 


EVIDENCES  OF   THE  MUTABILITY  OF  SPECIES 


115 


Fig.  72 


of  the  Hawk-eyed  moth.  Durhig  the  day  this  insect  sits  with  folded 
wings  on  the  willow,  or  other  tree.  The  eye  spot  and  the  rose-red  part 
of  the  wings  are  hidden,  and  the  moth  looks  like  a  group  of  dried  willow 
leaves.  This  is  its  protective  attitude,  by  which  it  wishes  to  escape 
observation.  But  if  disturbed  it  immediately  assumes  the  "terrifying 
attitude."  The  eye  spot  and  red  are  displayed,  the  thorax  is  arched, 
the  abdomen  curved  up.  This  is  accompanied  by  a  protruding  and 
retracting  of  the  front  of  the  body.  The 
movement  lasts  some  few  seconds,  or  half 
a  minute.  This  is  thought  to  frighten  the 
moth's  enemies.  The  eye  spot  may  sug- 
gest the  eye  of  some  much  larger  animal, 
while  the  energetic  motion  may  give  the 
impression  that  the  enemy  itself  is  about 
to  be  seized  and  devoui'ed.  But  does  the 
moth's  "terrifying  attitude"  really  frighten 
its  enemies  and  allow  it  to  escape?  Stand- 
fuss  tried  some  experiments  with  a  view 
to  settling  this  point.  He  gave  specimens 
of  the  moth  to  nightingale,  redbreast, 
black-cap,  and  other  birds.  Four  out  of 
five  were  obviously  frightened  when  the 
moth  assumed  the  "terrifying  attitude," 
and  left  it  alone  after  one  trial. 

The  "Kentish  glory  moth,"  a  British 
species,  passes  its  days  on  the  bark  of  the 
birch,  and  by  its  mimicry  of  colour  is 
thereby  protected  from  the  attack  of  birds, 

lizards,  and  other  creatures.  Nor  is  this  confined  entirely  to  the 
lower  animals  and  insects,  for  the  Bhils,  of  India,  practise  mimicry 
in  order  to  escape  their  enemies. '- 

Sexual  selection  is  a  secondarj-  cause  of  modification  of  species 
among  animals.  The  struggle  between  males  for  the  possession  of 
females  is  seen,  for  instance,  in  a  remarkable  degree  in  the  stags,  and 
the  deer,  and  the  sea-lions.  (See  Chapter  XVI.)  Sexual  selection 
explains  the  development  of  special   features,   which,   transmitted   in 


The  PhyUium  of  Ceylon,  an  in- 
sect, shaped  and  coloured  like  a  leaf. 
To  illustrate  protective  mimicry  in 
the  Ortkoptera.     X  -,%■ 


116 


DARWINIANA 


increasing  degree  through  a  series  of  generations,  probably  bring 
about  the  survival  of  the  fittest.  Sexual  selection  has  produced  the 
varying  colour  of  butterflies,  the  perfume  of  the  musk-deer,  the  song  of 
birds,  and  so  on;  and  everything  which  gives  an  advantage  or  advan- 
tages, to  a  plant  or  animal  over  its  competitors  in  the  struggle  for 
existence.  Dental  examples  may  be  given  as  follow:  The  male  frugiv- 
orous  monkeys  have  canines  which  are  larger  than  those  of  the  females 


Fig.  73 


Skulls  of  male  and  female  Old  World  monkeys.     X  i- 

(Fig.  73).  The  male  narwhal  and  the  male  dugong  have  tusks  which 
in  the  female  are  quite  insignificant  and  rudimentary.  The  musk- 
deer,  as  already  noticed,  possesses  huge  canines,  while  in  the  female 
musk-deer  the  canines  are  functionless.  The  male  Sus  Babirussa 
possesses  huge  tusks.  In  the  female  the  upper  canine  is  only  three- 
quarters  of  an  inch  in  length.  The  horse  possesses  canines,  these 
teeth  being  rudimentary  in  the  mare. 


EVIDENCES  OF   THE  MUTABILITY  OF  SPECIES  117 

Now  the  necessity'  for  food  and  the  power  to  obtain  it  are  probably 
the  strongest  stimulants  to  motion;  and  the  animal  which  readily 
adapts  itself  to  these,  wins  in  the  great  struggle  for  life.  The  new 
functions  which  have  to  be  discharged,  involve  changes  in  structure 
and  form  of  the  organs,  because  the  organs  exist  for  the  work  they 
have  to  do,  not  the  work  for  the  organs.  The  following  curious  and 
significant  fact  may  be  mentioned  in  this  connexion.  The  antlers 
of  some  species  of  deer  in  a  couple  of  months  will  grow  so  rapidly 
that  they  may  weigh  as  much  as  seventy  or  eighty  pounds.  This 
rapid  growth  necessitates  increased  blood  supply  to  the  parts,  and 
the  added  weight  on  the  frontal  bone  requires  greater  power  in  the 
muscles  and  ligaments  of  the  neck,  and  augmented  strength  in  the 
bones  to  Avhich  the  antlers  are  attached.  More  food,  therefore,  is 
required  by  the  animal.  This  requires  more  active  digestion,  and, 
therefore,  the  digestive  organs  become  structurally  modified. 

"Again,  man,  evolving  from  his  quadrupedal  and  anthropoid  prede- 
cessors, gradually  acquired  the  erect  position.  This  led  to  the  flatten- 
ing of  the  plantar  region  of  the  foot,  and  the  accompanying  growth  and 
development  of  the  os  calcis.  The  vertebral  column  became  curved 
in  such  a  way  as  to  best  sustain  the  weight  of  the  skull,  and  the  heavy 
brain  it  contained,  and  a  large  number  of  muscles  became  rearranged 
and  readjusted. "- 

Another  example  may  be  given.  The  ancestors  of  the  whale-bone 
whales  were  land  mammals,  which  had  short  fore  and  hind  limbs, 
broad  fiat  tails — like  the  beaver — many  teeth,  and  well-developed 
olfactory  organs.  They  were  all  omnivorous,  lived  in  marshes,  and 
fed  on  creatures  which  lived  both  on  the  land  and  in  the  sea.  Condi- 
tions more  and  more  adverse  to  life  came  on,  and,  under  the  influence 
of  Natural  Selection,  the  ancestors  of  the  whales  gradually  became 
dolphin-like  in  their  habits  and  structures,  took  to  living  in  fresh 
water  entirely;  and  then,  when  their  natural  enemies  the  ancient 
sea-lizards — whose  fossil  bones  are  still  discovered  here  and  there 
— had  become  extinct,  found  their  way  to  the  salt  water  of  the  seas, 
where  they  would  be  unmolested  by  their  foes,  and  other  land 
animals.  As  a  result,  the  fore  legs  became  flippers,  the  bones  being 
homologous.     Traces  of  hind  legs  can  be  found  in  some  whales  at  the 


lis  DARWINIANA 

present  day.  The  tail  became  divided  into  two  lobes,  the  head  became 
fish-like,  the  seven  cervical  vertebrae  became  fused,  the  skin  became 
hairless,  and  the  teeth — which  still  appear  in  the  rudimentary  organs 
in  whalebone  whales  —  disappeared,  and  fringes  of  baleen  were 
developed. 

Among  the  herbivorous  mammals  the  form  of  the  teeth  is  adaptively 
modified  for  grinding  instead  of  cutting. 

In  the  Carnivora,  the  intellect  is  more  highly  developed,  so  that  these 
creatures  can  stalk  their  prey,  and,  in  their  own  fashion,  think.  Their 
bodies  being  reduced  in  size,  their  muscular  strength  gradually  in- 
creased, their  teeth  and  claws  became  adapted  for  readily  attacking 
and  seizing  prey.  And,  last  of  all,  in  the  Primates,  the  limbs,  teeth, 
organs  of  digestion,  are  all  slightly  modified,  and  no  organ  of  defence 
or  attack  developed.  "The  reason  is  that  these  animals  took  to  an 
arboreal  life,  which  induced  but  few  variations  of  bodily  structure, 
the  most  important  being  opposable  thumbs  and  toes,  for  grasping. 
The  need  for  alertness  against  their  foes,  however,  sharpened  their 
wits,  and  the  necessity  for  mutual  help  and  combination  quickened 
their  social  instincts,  so  that  the  energy  which  in  the  herbivores  and 
carnivores  was  stored  in  muscle  and  limb  was  diverted  in  the  primates 
to  the  brain.  Thus  brain  power  conquered  brute  force,  and  skill  over- 
came strength.  "- 

Some  of  the  Primates  remained  arboreal  in  their  habits,  though 
approaching  bipedal  movements  in  walking.  Others  developed  a 
mode  of  progression  on  their  hind  limbs  only,  and  were  thus  enabled 
to  use  their  fore  limbs  for  throwing,  grasping,  or  handling  things.  This 
was  the  making  of  Man.  The  structural  difference  between  Man  and 
the  anthropoid  apes  is  very  slight  from  a  morphological  point  of  view. 
More  details  of  this  will  be  given  later  on  (see  Chapter  IX),  but  it 
lies  in  his  larger  and  more  complicated  thinking  apparatus — the  brain, 
with  its  wonderful  power  of  arranging,  classifying,  labelling,  and 
numbering  things,  coupled  with  the  faculty  of  enquiring  into  and 
discovering  their  origins,  and  the  invention  of  articles  of  commerce, 
art,  science,  and  war. 

Proofs  of  Derivation  of  Species.- — The  proofs  supplied  by  living 
beings  in  support  of  the  theory  of  their  common  descent  are  found 


EVIDE.XCES  OF   THE  AIUTABILITV  OF  SPECIES  119 

in  (i)  their  Embryology,  (2)  their  Morphology,  (3)  their  Classifications, 
(4)  their  Successio)i,  and  (5)  their  Distribiition. 

(i)  Embryology. — In  the  early  development  of  animals  it  is  impos- 
sible to  determine  whether  a  certain  embryo  is  that  of  a  bird,  a  lizard, 
a  dog,  or  a  human  being,  so  closely  do  they  outwardly  resemble  each 
other.  In  adult  life,  rudimentary  structures  frequently  remain  to 
point  to  this  close  affinity  of  living  beings.  Thus  such  dissimilar 
creatures  as  certain  snakes  and  whales  generally  possess  vestiges  of  a 
pelvis  and  hind  limbs,  all  foetal  whales  have  tooth  germs,  and  some 
non-flying  insects  have  wings  beneath  their  wing-cases. 

(2)  Morphology. — Certain  likenesses  of  anatomical  structure  exist 
in  widely  different  animals.  There  are  seven  cervical  vertebrae  in  the 
long-necked  giraffe  and  the  short-necked  pig;  the  ocular  apparatus  of 
the  lamprey  and  the  cat  is  controlled  by  six  similarly  arranged  and 
similarly  acting  muscles. 

(3)  Classifications. — Plants  are  classified  as  flowering  and  flower- 
less;  and  animals,  (a)  those  without  body  cavity,  as  the  monerou,  (b) 
those  with  body  cavity,  like  the  sea  anemone,  (c)  those  with  digestive 
cavity  separate  and  distinct  from  the  body  cavity,  as  the  implacental 
mammals  and  Man. 

(4)  Succession. — The  help  afforded  by  the  science  and  study  of 
palaeontology  is  very  great  in  regard  to  fossil  forms.  For  instance, 
the  one-toed  horse  is  shown  to  have  been  descended  from  the  five- 
toed  horse.  Birds  and  reptiles  have  descended  from  the  Archceopteryx, 
the  pigs  and  hippopotamuses  probably  through  the  Anoplotheriiirn; 
and  the  tapirs,  horses,  and  rhinoceroses  through  the  Palceotherium. 

(5)  Distribution. — All  living  things  have  their  definite  areas  of 
range.  Sloths  are  found  in  America,  chamois  in  the  Alps,  hippopota- 
muses in  Africa.  The  distribution  of  animals  is  due  to  the  slow  but 
ceaseless  migration  and  transport  of  living  things,  rendered  neces- 
sary by  their  rate  of  increase.  Islands  have  an  important  part  in  the 
problem  of  geographical  distribution,  as  in  the  marsupials,  which  are 
entirely  found  in  Australia,  a  few  being  found  in  South  America. 
And,  finalh',  the  agency  of  Man,  by  distributing  new  forms  and 
destroying  others,  has  done  much  in  the  same  direction. 

To  sum  up,  Darwin's  theory  means  that  species  have  been  modified 


120  DARWINIANA 

during  a  long  course  of  descent.  This  has  been  effected  chiefly  through 
Natural  Selection  of  numerous  successive  slight  favourable  variations, 
aided  in  an  important  manner  by  the  inherited  effects  of  the  use  and 
disuse  of  parts,  and  in  an  unimportant  manner — that  is,  in  relation 
to  adaptive  structures,  whether  past  or  present — by  the  direct  action 
of  external  conditions  and  "by  variations  which  seem  to  us,  in  our 
ignorance,  to  arise  spontaneously."^  *  ^ 


POST-DARWINIAN    THEORIES 

The  Mutation  Theory. — A  post-Darwinian  theorist  arose  in  the 
Netherlands  at  the  beginning  of  this  century  in  the  person  of  Hugo 
de  Vries,  who  initiated  what  is  known  as  the  Mutation  Theory,  an 
elaborate  study  of  certain  species  of  plants  which,  under  domesticated 
conditions,  were  able  to  produce  numerous  differences  in  size,  shape, 
and  colour  of  foliage,  method  of  growth,  etc.  His  work  was  called 
"Die  Mutations  Theorie."^^  He  believes  that  new  species  have 
been  produced  per  salttim,  not  by  Natural  Selection  and  Variation, 
which  was  the  main  principle  of  Darwinism.  By  artificial  means, 
Burbank,  of  America,  has  been  able  to  produce  variations  in  fruits, 
vegetables,  and  flowers,  but  not  new  species. 

The  main  argument  against  the  Mutation  Theory  is  that  these 
so-called  new  species  are  unable  to  hold  their  own  when  in  a  feral  con- 
dition, and  that  consequently  they  die  out;  whereas  those  produced 
by  Natural  Selection  and  Variations,  such  as  those  of  the  Protective 
Resemblance  and  Mimicry  of  butterflies  and  moths,  do  not. 

The  Mendelian  Theory. — Darwinism  has  been  replaced  in  the 
opinion  of  some  modern  Evolutionists  by  the  recently  revived  theories 
of  the  Abbot  Mendel,  of  Silesia,  who  flourished  about  a.d.,  1850, 
the  recrudescence  of  which  practically  synchronized  with  those  of 
de  Vries.  The  result  of  the  Mendelian  law  appears  to  be  a  tendency 
to  the  perpetuation  of  certain  pairs  of  characters  without  intermixture. 
Mendelian  phenomena  have  been  observed  in  peas,  mice,  rats,  snails, 
poultry,  rabbits,  and  some  other  plants  and  animals.  While  they 
furnish  interesting  materials  for  the  study  of  the  theory  of  heredity. 


POST-DARWIXIAN   THEORIES  121 

they  have  nothing  whatever  to  do  with  the  origin  of  species.'^  The 
results  of  Mendelian  experiment  are  not  constant.  A  law  of  heredity 
exists  in  the  case  of  everything  which  possesses  vital  elements,  identical 
in  every  particular,  no  matter  whether  it  be  of  an  animal  or  of  a 
vegetable  nature.  This  law  defines,  with  mathematical  accuracy,  the 
parental  qualities  which  will  be  handed  down  to  progeny.  Mendel 
the  monk,  observed  its  workings  in  his  cloistered  garden  in  Silesia 
when  he  interbred  plants  which  had  distinctive  and  peculiar  char- 
acteristics. The  strange  features  of  the  succeeding  generations  of 
certain  "crossed"  plants,  and  their  repetition  in  definite  and  sharp 
exactness,  induced  him  to  propound  a  law  which  has  since  borne  his 
name,  and  made  him  famous  wherever  scientists  discuss  the  principles 
of  heredity. 

Mendelian  law  affirms  that  in  cases  where  two  strongly  contrasting 
strains  are  crossed,  one  is  likely  to  prove  itself  a  "dominant,"  the 
other  a  "recessive." 

Thus  the  resulting  first  generation  of  offspring  would  be  all  similar 
in  appearance  to  the  predominating  strain,  otherwise  "dominants." 
Members  of  this  generation  beget  progeny  of  which  three-fourths 
follow  the  "dominant"  pattern,  and  one-fourth  show  the  characteristics 
of  the  weaker  grandparent  which  was  absolutely  absent  from  the  first 
immediate  generation.  In  the  third  generation  the  character  of  the 
weaker  member — the  "recessive" — reappears  in  the  offspring  of  those 
that  had  exhibited  it  in  the  second  generation,  and  remain  fixed, 
reproducing  themselves  indefinitely. 

Similarly,  the  characteristics  of  25  per  cent,  of  the  dominant  strain 
in  this  generation  become  fixed.  This  leaves  an  unfixed  50  per  cent. 
that  would  breed  another  generation  with  the  characteristics  partly 
fixed  and  partly  unfixed,  and  in  the  same  proportion  as  the  previous 
generation.  All  the  generations  that  followed  from  this  unfixed  d\\\- 
sion  would  be  like  the  third  generation  in  their  characteristics  and 
their  proportions. 

Results  of  Experiments. — In  order  to  test  the  truth  of  these 
statements  and  verify  this  law,  Dr.  Schroeder,  of  the  Department  of 
Agriculture  of  the  United  States  Government,  experimented  with 
rats  which,  being  very  fecund  animals,  offer  abundant  opportunities 


122  DARWIXIANA 

for  research.  There  are  two  plainly  marked  members  of  the  rat  family, 
the  plain  grey  and  the  "hooded."  The  first  is  of  a  solid  colour,  the 
other  being  white  with  a  black  head.  The  colours  are  the  distinctive 
points;  and  the  identification  of  the  two  kinds  of  offspring  easy  to 
determine. 

In  the  first  generation,  every  member  was  solidly  grey  like  the  domi- 
nant strain  of  the  parents.  Two  members  of  this  family  were  inter- 
bred— not  of  necessity  brothers  and  sisters — as  other  lines  had  been 
simultaneously  started.  In  this  case,  the  two  grey  rodents  of  the 
first  generation  produced  part  grey  and  part  "hooded"  offspring.  The 
"hooded"  rat  which  was  suppressed  in  the  first  generation,  appeared 
in  25  per  cent,  in  the  second.  These  "hooded"  rats  bred  "hooded" 
rats  in  the  following  generations.  Twenty-five  per  cent,  of  the  greys 
bred  all  greys,  a  remaining  proportion  still  having  the  unfixed  char- 
acteristics, repeating  the  proportions  of  the  second  generation.  This 
proved  the  correctness  of  Mendel's  law  of  heredity. 

If  a  black  Minorca  chicken  is  crossed  with  a  white  Leghorn,  all 
members  of  the  first  generation  will  be  white  in  colour.  The  second 
generation,  however,  will  be  25  per  cent,  black  as  the  original  Minorca, 
in  spite  of  the  fact  that  both  parents  are  white  in  colour.  The  white 
is  the  dominant  colour;  but  the  black  was,  so  to  speak,  "released"  in 
the  second  generation,  and,  thereafter,  produced  its  like.  In  certain 
strains  the  crossing  of  the  white  and  black  results  in  a  mottled  white 
and  black  chicken,  or  in  a  bluebird.  This  happens  when  neither 
peculiarity  is  able  to  establish  its  supremacy,  and  where  a  compromise 
is  possible. 

If  a  four-toed  and  a  five-toed  chicken  were  crossed,  the  results  failed 
to  follow,  because  the  supremacy  of  the  one  or  the  other  was  established, 
and  would  be  complete.  There  are  many  exceptions  to  the  rule,  also, 
in  individuals,  for  some  mark  their  offspring  strongly,  while  others 
fail  entirely  to  do  so.  Thus  a  tailless  game-cock  will  fail  to  produce 
one  tailless  bird  when  crossed  with  tailed  hens,  yet  another  similar 
game-cock  will  produce  50  per  cent,  of  tailless  progeny  from  the  same 
hens. 

Through  the  operation  of  this  law  a  rose  in  the  garden  may  develop 
traits  of  shape  and  features  of  colour  which  were  not  indicated  by  its 


POST-DARWINIAN   THEORIES  123 

parents;  horses  and  cattle  revert  to  an  early  ancestry.  Black-haired 
parents  may,  and  do,  beget  blond  or  red-haired  children.  A  man  of 
imusual  intellect  is  developed  very  often  in  a  family  the  members  of 
■which  are  all  stupid. 

"This  general  law  of  heredity  is  intended  as  a  guide  for  the  farmer, 
the  stock  raiser,  and  the  father  of  a  family.  From  it  he  may  forecast 
the  future,  and  prevent  the  recurrence  of  the  undesirable."" 

Professor  Alfred  Russell  Wallace"  writes:  "As  playing  any  essential 
part  in  the  scheme  of  organic  development,  the  phenomena"  above 
mentioned  "seem  to  be  of  the  very  slightest  importance.  They  arise 
out  of  what  are  essentially  abnormalities,  whether  called  varieties, 
'mutations,'  or  'sports.'  These  abnormalities  are  very  rare  in  a  state 
of  Nature,  as  compared  with  the  ever-present  individual  variability, 
ample  in  amount  and  affecting  every  part  or  organ,  which  furnishes 
the  material  both  for  Man's  and  for  Nature's  selection.  The  very 
fixity  of  these  abnormalities,  and  the  small  number  of  the  characters 
affected  by  them,  as  well  as  their  rarity,  all  show  them  to  be  the  refuse 
material  of  Nature's  workshop,  as  proved  by  the  fact  that  none  of 
them  ever  maintain  themselves  in  a  state  of  Nature." 

It  may  be  added  that  the  Darwinian  theory  of  evolution,  and  this 
theor}'  only,  can  be,  at  present,  applied  to  the  evolution  of  the  teeth, 
and  that  in  all  probability  the  Lamarckian,  Mutationist,  and  Mendelian 
theories  are  predestined,  in  this  sense,  to  fail,  or  in  any  degree  to 
approach,  the  deductions  of  our  Great  Englishman. 

References 

1.  Bateson.  "Materials  for  the  Study  of  Variation  Treated  with  Especial  Regard  to  Discon- 
tinuity in  the  Origin  of  Species, "  1894. 

2.  Clodd.    "The  Story  of  Creation,"  1888. 

3.  Darwin.     "Descent  of  Man,  "  1871. 

4.  Darwin.     "  Origin  of  Species,  "  1859. 

5.  Darwin.    "The  Variations  in  Animals  and  Plants,"  1868. 

6.  Drummond.    "  Natural  Law  in  the  Spiritual  World,  "  1888. 

7.  Haeckel.    "  The  Evolution  of  Man,  "  1874. 

8.  Headley.    "  Life  and  Evolution, '    1906. 

9.  Lamarck.     "Philosophic  Zoologique,"  1809. 

ID.  Lamarck.     "Histoire  Naturelle  des  Animaux  sans  Veitebres, "  1S15. 
II.  Linnaeus.     " Systema  Nalura:,"  ij^$. 


124  DARWINIANA 

12.  "Living  Races  of  Mankind,"  1906,  vol.  i. 

13.  Lock,  R.  H.     "Variation,  Heredity,  and  Evolution,"  1906. 

14.  Milnes  Marshall.     "The  Darwinian  Theory,"  1894. 

15.  Du  Puy,  W.  A.    "  Mendelism,  "  New  York  Tribune,  1909. 

16.  Turner,  J.  G.    "Heredity  in  Teeth  and  Jaws,  "  Royal  Dental  Hospital  Reports,  1912. 

17.  Russell  Wallace.     "The  Present  Position  of  Darwinism,"  The  Contemporary  Review,  August, 
1908. 

1 8 .  Russell  Wallace.    ' '  Darwinism , "  1 90 1 . 

19.  Saville  Kent.    "Manual  of  the  Infusoria,"  vol.  i. 


CHAPTER    VI 
THE  IMPLANTATION  AND  REPLACEMENT  OF  TEETH 

The  Implantation  of  Teeth  in  Fishes,  Reptiles,  and  Mammals. — The  Replacement  of  Teeth  in 
Fishes,  Reptiles,  and  Mammals. — Vertical  and  Oblique  Successions. — Absorptions:  Physio- 
logical and  Pathological. 

Second  onl}-  in  importance  to  the  size,  shape,  and  position  of  the 
teeth,  is  their  attachment  by  a  fibrous  membrane  to  bone  or  cartilage 
of  the  jaw,  as  the  case  demands;  for  no  matter  how  well  suited  an  organ 
may  be  for  the  requirements  of  its  possessor  in  the  comminution  of 
food,  in  seizing  and  holding  prey,  and  in  fighting  its  natural  enemies, 
unless  a  firm  foundation  is  established  and  it  is  securely  fixed  in  the 
soft  or  hard  parts  close  by,  it  is  a  useless  organ. 


IMPLANTATION    OF    TEETH 

In  Fishes. — The  great  diversities  in  the  shapes  in  the  teeth  of  fishes, 
have  already  been  described,  and  it  is  again  this  enormous  group  of 
animals  that  offers  many  varieties  of  implantations.  The  simplest 
of  all  is  seen  amongst  the  sharks  and  rays,  where  the  teeth  are  fixed 
by  ligaments  to  the  margins  of  the  jaws.  On  the  marginal  surfaces 
of  the  latter  there  are  long  grooves  to  give  attachment  to  these  liga- 
ments which  contain  the  teeth  embedded  in  them.  This  is  the  simplest 
form,  the  teeth  merely  being  surrounded  by  a  thickened  sheath  of 
epithelial  and  dermal  tissue,  and  their  bases  widened  to  serve  as  a 
method  of  support. 

A  more  complicated  variety  occurs  in  what  is  called  the  "bone  of 
attachment,"^  in  which  a  special  building  up  of  osseous  material 
fastens  the  teeth  to  the  oral  bones.  Thus,  in  the  mouths  of  the  eel 
and  the  wolf-fish,  and  in  man}'  other  fishes,  is  found  the  "bone  of 
attachment."     In  the  case  of  the  eel,  the  tooth  is  anch\losed  to  the 


126  THE  IMPLANTATION  AND  REPLACEMENT  OF   TEETH 

jaw,  that  is  to  say,  the  tissues  of  the  tooth  proper  become  blended 
with  the  tissues  of  the  bone  proper.  This  is  the  commonest  method  of 
attachment  in  the  fishes,  and  is  exempHfied  in  the  eel  and  the  hake. 
Before  complete  anchylosis  of  the  tooth  has  occurred  during  develop- 
mental periods,  it  is  held  to  the  jaw  by  a  ligament  either  to  the  flat 
surface  of  the  bone  or  to  an  eminence,  or  even  to  a  depression  in  the 
osseous  material. 

A  modification  of  this  method  is  known  as  the  "hinge"  form,  in 
which,  as  in  the  pike  or  the  hake,  one  side  of  the  tooth  is  not  anchylosed, 
but  is  fixed  to  the  "bone  of  attachment"  by  means  of  a  hinge  of  elastic 
tissue  fibres.  The  other  side  of  the  tooth  is  also  not  anchylosed  to 
the  "bone  of  attachment,"  but,  being  widened  at  the  base,  is  placed 
in  apposition  to  the  "bone  of  attachment"  on  account  of  the  virtue 
of  the  hinge  on  the  other  side  of  the  tooth.  The  method  is  a  most 
ingenious  one  for  allowing  some  predatory  fishes,  like  the  hake  and 
the  pike,  to  grasp  their  living  prey,  and  to  prevent  their  food  from 
slipping  away  from  them;  for  in  every  instance,  is  the  hinge  fixed  on 
the  lingual  side  of  the  tooth,  and  the  teeth,  therefore,  can  bend  inwards. 

Amongst  fishes  also,  the  method  of  implantation  known  as  gomphosis 
— which  implies  the  means  by  which  a  nail  is  driven  into  a  piece  of 
wood — obtains.  In  this  division  there  are  (i)  a  simple  fibrous  gom- 
phosis, (n)  a  double  gomphosis,  and  (in)  a  bony  gomphosis.  With 
regard  to  the  first,  the  rostral  teeth  of  Pristis,  the  incisor-like  teeth 
of  Sargus,  and  the  teeth  of  haddock  are  noticeable.  It  may  be  here 
noted  that  the  position  of  the  rostral  teeth  of  the  sawfish,  imbedded 
in  cylindrical  cavities  on  the  lateral  edges  of  the  rostrum  by  means  of 
a  fibrous  tissue,  and  therefore  outside  the  mouth  entirely,  is  a  special- 
ized reversion  to  a  condition  which  probably  obtained  in  the  ancestors 
of  all  fishes.  The  teeth  of  these  creatures,  in  their  most  primitive 
condition,  correspond  exactly  in  structure  with  the  small  osseous 
enamel-capped  granules  of  the  skin,  as  in  the  sharks  and  rays,  thus 
demonstrating  that  teeth  were  originally  simple  external  organs,  and 
also  showing  that  teeth  were  homologous  with  the  placoid  scales  of 
fishes. 

As  an  example  of  bony  gomphosis,  the  teeth  of  the  mackerel — 
which  are  but  slightly  implanted — may  be  cited,  where  a  small  gutter 


IMPLANTATIOX  OF   TEETH  127 

of  bone  intervenes  between  the  teeth  internally  and  the  bone  of  the 
jaw  externally. 

The  most  complicated  method  of  fixation  known  amongst  the  fishes 
will  naturally  be  found  in  the  mouths  of  those  which  have  the  hardest 
work  to  do  from  the  dental  point  of  view.  Hence,  it  is  not  surprising 
that  the  file-fish,  which  has  already  been  mentioned,  should  possess, 
in  its  incisor  region  a  most  excellent  method  for  the  implantation  of 
its  rodent-like  teeth,  for  the  purpose  of  eflficiently  chiselling  through 
the  shells  of  oysters  and  other  molluscs.  In  this  instance  of  double 
gomphosis  the  jaw  and  the  tooth  reciprocally  receive,  and  are  received 
by  each  other,  a  buttress  of  bone  beneath  the  tooth  spreading  out  in 
the  form  of  a  stud,  to  form  a  strong  attachment.^ 

A  final  example  may  be  given  in  the  teeth  of  the  Diodoii  or  Tetradon, 
which  are  firmly  fixed  on  the  margin  of  the  jaw,  the  structures  of 
both  passing  insensibly  into  each  other. 

In  Reptiles. — Amongst  the  reptiles,  the  method  of  attachment  is  by 
anchylosis.  Simpler  as  the  teeth  are  in  shape  and  size,  so  is  their  attach- 
ment. When  a  reptile,  like  the  Varaiius,  has  its  teeth  anchylosed  near 
the  summit  of  the  margin  of  the  jaw,  a  pleurodont  condition  obtains; 
where,  however,  the  teeth  are  fixed  on  the  summit  of  the  jaw,  as  in 
the  iguana,  an  acrodont  condition  is  spoken  of.  The  crocodile,  amongst 
the  reptiles,  differs  probably  more  than  any  of  the  others  in  being  a 
thecodont  reptile.  Here  the  teeth  are  apparently  socketed,  and  not 
really  anchylosed,  as  each  tooth  is  surrounded  by  a  sheathed  condition 
of  the  soft  tissues. 

In  Mammals. — Amongst  mammals,  sockets  are  generally  found.  They 
may  be  deep  or  shallow,  wide  or  narrow,  under  varying  circumstances, 
those  occurring  in  the  incisor  region  of  the  jaws  of  rodents  being  deepest 
for  obvious  reasons.  Anchylosis  is  never  found  amongst  the  mammals, 
except  on  the  authority  of  Sir  William  Flower,  in  the  mandibular 
incisors  of  adult  shrews,  and  extremely  rarely,  as  a  pathological  condi- 
tion, in  the  case  of  Man.  Not  more  than  ten  cases  of  anchylosis  in 
Man  have  been  recorded,-  and  in  one,  which  came  under  the  notice 
of  the  author,  it  was  associated  with  a  disease  of  the  bones  of  the 
face  called  leoutiasis  osseiDii. 


128 


THE  IMPLANTATION  AND  REPLACEMENT  OF   TEETH 


THE    REPLACEMENT    OF    TEETH 


Fig.  74 


To  complete  this  portion  of  the  subject,  a   few  words  must  now  be 
said  about  the  Succession  of  teeth,  for  it  ought  already  to  have  been 

clear  that  some  teeth  are  shed  early, 
others  taking  their  place;  others  may 
remain  throughout  the  life  of  the 
animal. 

In  Fishes. — In  fishes,  again,  there 
exists  a  variety  of  methods  of  succes- 
sion. For  instance,  in  the  sharks  and 
rays  there  is  a  continuous  replacement 
of  teeth,  that  is  to  say,  when  one 
tooth  has  been  shed,  another  tooth 
takes  its  place,  and  so  on  throughout 
the  life  of  the  animal.  This  is  known 
as  a  Polyphyodont  condition.  The 
teeth  of  the  sharks  and  rays,  which 
are  implanted  in  ligament,  exhibit  this 
continuous  succession  extremely  well. 
It  is  probable  that  all  fishes  have  a 
continuous  succession  of  teeth,  but  the 
condition  may  be  divided  into  three 
classes,  in  which  there  is  {i)  a  Trans- 
verse continuous  succession,  as  in  the 
Carcharias,  the  word  meaning  trans- 
verse to  the  long  axis  of  the  mouth; 
(Ji)  a  Longitudinal  succession,  as  in 
the  Heterodontis  {Cestracion  Philippi), 
where  the  teeth  succeed  one  another 
from  behind  forward  and  move  outward  in  an  antero-posterior  direction, 
passing  in  a  line  which  corresponds  to  the  long  axis  of  the  mouth;  and 
{Hi)  in  a  Vertical  direction,  as  in  the  file-fish,  where  an  example  is  given 
of  an  isolated  vertical  continuous  succession,  and  in  the  Diodon,  which 
affords  an  illustration  of  a  fused  vertical  continuous  succession. 


Jaws  of  the  Port  Jackson  shark,  Hetero- 
dontis {Cestracion  Philippi).  X  f.  De- 
velopment proceeds  from  within  outwards. 
The  jaws  are  widely  distended,  and  owing 
to  their  cartilaginous  nature,  have  become 
somewhat  distorted  as  a  result  of  the 
drying  of  the  specimen. 


THE  REPLACEMENT  OF   TEETH 


129 


The  mandible  of  the  Alepidosaunis  ferox  exhibits  (Fig.  75)  a  curious 
and  interesting  physiological  provision,  in  case  of  accident  or  injury 
to  the  mouth.  Toward  the  front  of  the  jaw  there  are  two  strong, 
pointed  teeth,  longer  than  the  rest,  whose  main  function  is  evidently 
one  of  prehension  of  food.  At  the  base  of  each  tooth,  enclosed  in  a 
horizontal  cavity  of  reserve,  lies  a  tooth  similar  in  size  and  shape. 
If  one  or  both  of  the  functional  prominent  teeth  happened  to  get 
knocked  out,  the  successional  tooth,  lying  in  a  horizontal  plane,  at 
once  is  ready  to  assume  a  vertical  position,  and  actually  takes  the 
place  of  the  lost  functional  tooth  in  an  incredibly  short  space  of  time. 
According  to  the  late  Dr.  Boulenger,  of  the  Natural  History  Museum, 
this  may  occupy  only  a  few  minutes  less  than  half  an  hour. 


Fig.  75 


Mandible  of  Alepidosaunis  ferox. 


It  is  known  in  this  connexion,  that  if  a  poison  fang  of  a  viper  is 
lost,  another  can  replace  it  in  a  quarter  of  an  hour. 

In  Reptiles. — In  the  reptiles,  there  is  a  continuous  vertical  succes- 
sion, as  exemplified,  for  instance  by  the  crocodile  and  the  lizard,  also 
by  the  extinct  gigantic  creature  known  as  the  Diplodociis. 

In  Mammals. — Mammals  exhibit  what  are  known  as  {i)  a  Vertical 
succession,  and  («)  an  Oblique  succession.  Mammals  may  be  either 
monophyodont  or  diphyodont,  that  is  to  say,  they  may  have  one  set 
of  teeth,  or  have  two  sets  of  teeth.  Of  the  former,  the  Australian 
water  rat  and  the  English  rat  are  good  examples.  Here  the  incisors 
9 


130 


THE  IMPLANTATION  AND  REPLACEMENT  OF   TEETH 


are  continuously  growing,  they  grow  from  "persistent"  pulps;  as  their 
cutting  surfaces  get  worn  down  by  gnawing  wood,  etc.,  so  more  tissue 
is  formed  at  the  root,  and  the  apical  portion  remains  always  widely 
patent. 

It  is  probable  also  that  the  kangaroos  and  Australian  mammals 
are,  generally  speaking,  monophyodont  with  closed  apical  foramina 
to  their  teeth,  but  a  diphyodont  condition  is  usual  in  other  mammals, 
the  "milk  teeth"  lasting  for  a  short  period  of  the  animal's  life,  and 
being  succeeded  by  a  permanent  series.  In  all  these  cases  the  teeth 
are  replaced  more  or  less  vertically. 

The  jaws  of  the  elephant,  in  the  order  Prohoscidea,  however,  show 
an  oblique  succession  in  the  molar  region.  This  animal  throughout 
its  lifetime  has  altogether  only  twenty-four  molars,  and  when  it  is 
remembered  that  an  elephant  may  live  for  three  hundred  and  fifty 
years,  it  can  be  readily  understood  that  it  will  not  require  the  whole 
of  the  grinding  surface  of  these  molars  for  use  at  the  same  time.  There- 
fore, what  is  known  as  an  oblique  succession  of  the  teeth  is  produced, 
in  which  a  small  portion  only  of  the  morsal  surface  of  the  molars  is 
brought  into  function  at  one  and  the  same  time.  As  this  portion  gets 
worn  down  the  posterior   portions  of  the  teeth  come  into  position.^ 


Fig. 

76 

HhF    iF^^IV    r™m 

Fig.  77 


Radiograph  of  right  side  of  the  mandible 
showing  absorption  of  the  roots  of  the  second 
deciduous  molar  and  its  replacement  by  the 
second  premolar.     Cf.  Fig.  77. 


Absorption  of  the  roots  of  the  second  decid- 
uous molar  and  no  replacement  by  a  premolar. 
The  first  permanent  molar  has  been  ex- 
tracted. 


Dental  Absorption  in  Man. — In  Man  a  limited  vertical  succession 
obtains,  the  roots  of  the  deciduous  teeth  being  absorbed,  it  is  generally 
believed  by  means  of  a  special  tissue  to  which  the  name  "absorbent 


THE  REPLACEMENT  OF   TEETH  131 

organ"  has  been  applied.  It  is,  here,  a  physiological  process,  assisted 
by  the  gradual  development  and  eruption  of  the  successional  teeth. 
At  times,  however,  there  is  no  displacing  tooth,  yet  the  absorption 
of  the  roots  proceeds  as  usual.  The  skiagram  (Fig.  76)  shows  such 
a  condition  in  the  mouth  of  a  gii;l  of  fourteen  years.  The  second 
right  mandibular  molar  of  the  deciduous  series  has  almost  completely 
lost  its  roots  and  there  is  no  second  premolar  beneath.  Fig.  ']']  placed 
by  its  side  exhibits  a  normal  condition. 

It  is  not  quite  clear  whether  a  special  organ  does  exist.  Soft  tissue 
is  often  seen  attached  to  the  partially  resorbed  roots  of  deciduous 
molars,  which,  histologically,  resembles  granulation  tissue,  containing 
numerous  myeloid  cells  which  excavate  the  dentine  by  a  kind  of  phago- 
cytic action,  and  thereby  produce  the  foveolae  of  Howship.-  Precisely 
the  same  occurs,  from  a  microscopical  point  of  view,  in  the  pathological 
absorption  of  the  permanent  roots.  Here,  however,  the  process  repre- 
sents only  one  of  the  terminations  of  inflammation  of  the  periodontal 
membrane,  and  may  be  localized  to  one  tooth,  or  be  more  or  less 
general  throughout  the  whole  dental  series. - 

Choquet,^  in  an  important  address,  gives  a  chronological  account 
of  the  theories  which  have  been  held  regarding  the  absorption  of  the 
roots  of  the  deciduous  teeth,  from  the  beginning  of  the  Eighteenth 
Century,  and  describes  the  "mechanical"  theory  of  Bunon,  which 
was  replaced  by  the  "organic"  theory  of  Burdet,  who  was  the  pre- 
cursor of  the  theories  of  Delabarre  and  Sir  John  Tomes.  He  agrees, 
however,  with  Redier,-*  who  advances  the  belief  that  this  absorption 
is  caused  by  a  process  of  bone  inflammation  the  effect  of  which  is 
alternately  to  absorb  old,  and  produce  new  bone,  and  he  verifies  this 
belief  by  personal  experimentation.  Redier's  theory  is  considered  by 
this  author  as  no  longer  an  hypothesis,  but  as  an  established  fact. 

References 

1.  Choquet.  "Etude  sur  la  Resorption  des  racines  des  dents  temporaires,  quel  en  est  le  Processus 
physiologique?"    Handbook  of  the  Fifth  Internalional  Dental  Congress,  191 1. 

2.  Hopewell-Smith.  "Histology  and  Patho-histology  of  the  Teeth  and  Associated  Parts."  1903. 
"A  Case  of  Infective  Disease  of  the  Jaws  Associated  with  Absorption  of  the  Teeth,"  Proc.  Roy. 
Soc.  of  Medicine,  1909. 

3.  Owen.     "Odontography,"  1840. 

4.  Redier.     "Precis  de  Stomatologie,"  1909. 

5.  Tomes.     "  A  Manual  of  Dental  Anatomy,  "  1898. 

6.  Wiedersheim  and  Parker.     "Comparative  Anatomy  of  the  Vertebrates,"  1907. 


CHAPTER    VII 
DENTAL   HOMOLOGIES 

The  jMeaning  of  Homology. — Kinds  of  Homology. — Examples. — Meaning  of  Analogy. — Examples. — - 
Difficulties  of  Homology. — Examples. 

The  reader  is  now  prepared,  after  discussing  the  nature,  the  func- 
tions, the  number,  position,  shape,  attachment,  and  succession  of 
teeth  generally,  to  understand  their  homologies.  By  this  is  meant 
that  he  will  be  enabled  to  determine  approximately  the  denomina- 
tion of  any  teeth  in  any  given  skull.  Thus,  it  has  already  been  men- 
tioned that  in  the  mouth  of  the  giraffe,  as  in  other  ungulates,  there 
are,  in  the  front  of  the  mandible,  eight  small  teeth  grouped  closely 
together,  the  outermost  of  which,  different  in  shape  to  the  others, 
is  used  for  tearing  leaves  from  the  twigs  on  which  they  grow.  This 
fourth  outer  tooth  has  much  the  appearance  of  a  modified  incisor, 
but  in  reality  it  is  a  canine,  although  it  bears  no  resemblance  to  such 
a  tooth,  and  does  not  in  the  least  conform  to  the  definition  already 
given  of  a  canine.  Reverting  for  a  moment  to  that  definition,  it  will 
be  remembered  that  "a  canine  is  that  tooth  behind  the  intermaxillary 
suture,  if  it  is  not  too  far  behind;"  and  the  lower  canine  is  the  tooth 
that,  in  occlusion,  passes  immediately  in  front  of  the  upper  one.  In 
the  case  of  the  giraffe,  however,  there  is  no  upper  canine  at  all. 
This  animal  has,  as  usually  obtains  in  many  other  herbivorous  types, 
no  maxillary  front  teeth,  but  bites  on  a  thick,  fibrous  pad  of  gum  in  the 
front  portion  of  the  upper  jaw.  Is  it  possible,  therefore,  to  determine 
whether  this  tooth  is  a  canine  or  whether  it  is  an  incisor?  One  is  helped 
by  consideration  of  the  homology  of  the  teeth  generally. 

HOMOLOGY 

Homology  is  the  proof  of  the  common  origin  of  two  organs.^  It 
may  be  expressed,  in  other  words,  as  "the  morphological  identity  of 
representative  parts  in  different  animals." 


HOMOLOGY  133 

Kinds. — There  are  four  kinds  of  homology: 

(i)  Radial  homology,  exemplified  in  the  starfish,  in  which  all  por- 
tions of  the  body  bear  an  anatomical  resemblance,  and  radiate  from 
a  common  centre. 

(2)  Serial  homology,  as  exemplified  in  the  lobster  or  centipede, 
which  creatures  exhibit  bilateral  symmetry  in  the  abdominal  segments 
of  their  bodies. 

(3)  Lateral  homology,  which  means  structural  identity  of  organs 
on  both  sides  of  the  body,  such  as  the  antennae  of  the  butterflj^;  and 

(4)  Vertical  homology,  as  in  the  front  and  hind  limbs  of  the  verte- 
brates generally,  a  term  which  means  the  similar  structural  identity 
existing  between  anterior  and  posterior  appendages  on  the  same  side 
of  the  body. 

Dental  Homology. — Dental  homology  falls  under  the  third  division;  it 
means  the  correspondence  in  relative  structure,  position,  proportion, 
value,  and  development  of  the  teeth,  but  not  in  shape  or  size  or  function. 

Teeth  are  said  to  be  homologous  with  dermal  spines,  as,  for  instance, 
the  placoid  spines  or  the  scales  of  the  dog-fish.^  Their  structure  and 
development  is  similar,  if  not  identical.  If  a  vertical  section  be  made 
through  the  head  of  a  young  dog-fish,  and  it  is  examined  microscopically, 
it  is  impossible  to  say,  except  by  position,  which  is  a  dermal  spine, 
and  which  is  a  young  functional  tooth.  "The  basis  from  which  the 
matrix  of  a  tooth  of  a  shark  and  the  antler  of  the  deer  grows,  is  homo- 
logically  the  same."-  The  homologies  of  the  mammalian  skeleton 
were  first  studied  by  Buffon,  who  was  born  in  1707,  and  died  in  1788. 
The  whole  subject  is  an  abstruse  and  yet  very  fascinating  one.  \Mth 
regard  to  special  dental  homologies  enormous  difficulties  exist.'- >  In 
order  to  get  a  clear  conception  of  the  terms  "homology"  and  "analogy," 
examples  may  be  given  as  illustrations. 

Examples  of  Homology. — (i)  Teeth  and  dermal  spines,  as  already 
mentioned. 

(2)  Different  organs,  like  the  arm  of  a  man,  the  foreleg  of  a  dog, 
and  the  wing  of  a  bird,  which  are  morphologically  similar.  If,  for 
instance,  the  bony  framework  of  the  arm,  the  foreleg,  and  the  wing 
be  examined,  it  will  be  found  that  there  is  in  each  case — in  these  differ- 
ent creatures,   man,   dog,   and  bird — a  humerus,   a  radius,   and  ulna, 


134 


DENTAL  HOMOLOGIES 


a  series  of  carpal  bones,  and  a  series  of  metacarpal  bones.  They  are 
identical  from  the  point  of  view  of  anatomical  structure,  though,  of 
course,  it  is  obvious  that  they  vary  in  size  and  in  shape.  They  are 
not  analogous,  because  they  are  used  for  different  purposes. 


Fig.  78 


Diagram  to  illustrate  homology:  A,  the  bones  of  the  right  arm  of  a  man;  B,  of  the  right  leg  of 
a  lion;  C,  of  the  right  wing  of  a  bird;  H,  the  humerus;  R,  the  radius;  U,  the  ulna;  C,  the  carpus; 
M,  the  metacarpus;  P,  the  phalanges. 

ANALOGY 


Analogous  organs  are  different  organs  which  perform  similar  func- 
tions. Two  illustrations  may  be  given:  First,  the  denticulate  incisors 
in  the  lower  jaw  of  the  Galeopithecus,  and  the  epithelial  papillae  of 
the  tongue  of  the  cat;  and  secondly,  the  wing  of  a  bird  and  the  wing 
of  an  insect.  It  requires  no  effort  of  the  imagination  to  conceive  that 
the  pectinate  incisors  of  the  Galeopithecus  differ  very  remarkably, 
anatomically,  from  the  lingual  papillae  of  the  cat,  as  also  the  wing  of 


ANALOGY  135 

a  bird  differs  morphologically  from  the  wing  of  an  insect.  They  are 
analogous  organs,  however,  because  they  perform  the  same  function, 
namely,  that  of  combing  the  fur  in  the  first  instance,  and  flying,  in 
the  second  instance. 

Finally,  examples  of  both  homology  and  analogy  may  be  cited.  The 
leg  of  a  man  and  the  hind  leg  of  a  dog  are  both  homologous  and  analo- 
gous, being  structurally  identical  and  performing  the  same  functions. 
Also,  the  poison  dorsal  and  opercular  spines  of  the  weaver  fish. 

As  a  rule,  it  is  not  a  difificult  matter  to  decide  the  homology  of  a 
certain  tooth.  In  connection  with  the  fourth  outermost  tooth  of  the 
giraffe,  sheep,  ox,  etc.,  however,  the  reader  knows  that  in  the  typical 
mammalian  placental  dentition  there  are  three  incisors  only,  and  the 
fourth  tooth,  which  does  not  supply  an  answ^er  to  the  definition  already 
given  of  the  lower  canine,  must  be  this  tooth  on  account  of  its  homology 
in  other  animals. 

The  classical  definition  of  the  upper  canine  holds  good  with  regard 
to  the  jaws  of  dog  and  man  and  many  animals.  A  problem,  however, 
occurs  in  the  jaws  of  the  mole  with  regard  to  its  teeth,  for  the  upper 
canine-like  tooth  is  in  front  of  or  within  the  intermaxillary  suture, 
Avhile  the  lower  canine-like  tooth  occludes  behind  the  upper  one.  Hence, 
while  the  upper  tooth  may  be  analogous  with  the  canine  in  mammals, 
on  account  of  its  value  as  a  seizing  tooth,  its  anomalous  position  makes 
it  a  very  large  fourth  incisor.  Regarding  the  mandibular  canine-like 
tooth,  the  fourth  incisiform  tooth  must  be  regarded,  if  this  definition 
is  correct,  as  a  true  canine,  although  the  first  premolar,  larger  than  the 
others,  is  functionally  the  true  canine.  The  dental  formula  of  the 
mole  is,-*  as  has  already  been  pointed  out,  I  |  C  I  Pni  t  M  |  x  2  =  44. 

In  some  other  members  of  the  Insectivora,  the  premolars  are  canini- 
form  in  shape.  The  first  lower  premolar  and  the  upper  third  incisor 
are  like  canines  in  appearance;  and  again  other  groups  have  no  tooth 
specially  pointed  or  specially  functional.  It  is  probable  that  no  man- 
dibular incisor  becomes  canine-like  to  oppose  an  upper  canine. 

References 

1.  Bateson.     " Materials  for  the  Study  of  Variations, "  1894. 

2.  Owen.    "On  tlie  Anatomy  of  the  Vertebrates, "  1868. 

3.  Schwalbe.  "Ueber  Theorien  der  Dentition,  Verhandl.  d.  anat.  Gesellschaft.  Anat.  Anzeiger, " 
1894. 

4.  Tomes.     "A  Manual  of  Dental  Anatomy,"  1898. 


CHAPTER    VIII 
THE   EVOLUTION   OF   THE   MAMiMALIAN   CROWNS 

The  Production  of  the  Complexities  of  Patterns  of  the  MammaUan  Crowns. — The  Concrescence 
Theory;  Evidence  in  Favour. — E.Kamples. — The  Tritubercular  Theory. — The  Work  of  Cope, 
Osborn,  and  Wortman. 


THE    PRODUCTION    OF    THE    PATTERNS    OF    MAMMALIAN 

CROWNS 

It  is  not  necessary,  after  what  has  already  been  said,  to  emphasize 
the  fact  that  the  back  teeth  of  most  mammals  present  a  very  compli- 
cated pattern  from  their  coronal  point  of  view.  How  is  it  that  they 
present  these  complex  patterns?  Why,  for  instance,  is  it  that  the 
molars  of  the  elephant — of  which  two  species  only  remain,  the  Indian 
and  the  African — are  not  the  same?  In  other  words,  "How  has  it 
come  about  that  the  molars  of  mammalian  teeth  present  a  great  number 
of  cusps?"     The  problem  has  puzzled  the  minds  of  many  biologists. 

At  the  present  time,  it  may  be  said,  briefly,  that  three  schools  of 
thought  are  divided  as  to  the  origin  of  the  cusps  of  the  mammalian 
teeth.  These  may  be  known,  first,  as  the  Fusionists,  secondly,  the 
Trituberculists,  and  thirdly,  the  Multituberculists.''  The  former  hold 
that  through  the  shortening  of  the  jaws  the  haplodont  teeth  of  the 
primitive  type  become  fused,  and  ultimately  molariform  in  shape. 
This  is  the  theory  of  Rose,^  Virchow,"  and  Kiikenthal,*  its  modern 
exponent  being  Marett  Tims.''  The  latter  hold  that  simple  haplodont 
teeth  have  cusps  developed  upon  them.  It  is  necessary  to  consider 
the  various  ideas  of  the  two  first-named  schools  of  thought. 

THE    CONCRESCENCE    THEORY 

If  the  theory  of  the  fusion  of  haplodont  teeth  was  correct,  one  would 
expect  to  find  that  the  molars  or  back  teeth  of  Mesozoic  animals  would 
be  of  a  simple  t^'pe  and  pattern,  and  those  of  an  earlier  period  in  the 


THE  CONCRESCENCE   THEORY 


137 


Fig.  79 


history  of  the  world  still  again  simpler;  but  this  is  not  the  case.  The 
earliest  known  mammal  is  probably  the  Microlestes,  the  progenitor  of 
the  rat  kangaroo  of  Australia.  The  molar  teeth  here  are  somewhat 
similar  to  the  molar  calcified  teeth  of  the  Ornithorhynchus,  and  show 
no  signs  whatever  of  a  simpler  formation.  Still,  the  reader  is  inclined 
to  ask,  "Why  do  the  supernumerary  and  supplemen- 
tary teeth  of  the  Primates  nearly  always  approximate 
the  shape  of  a  cone?" 

Is  it  unreasonable  to  suppose  that  these  ill-formed, 
stunted,  peg-shaped  teeth  are  really  an  attempted 
expression  of  Nature,  of  certain  atavistic  proclivities 
on  the  part  of  Man,  and  that  in  themselves  they 
may  be  considered  to  be  evidences  of  his  reptilian 
descent?  (Fig.  79).  Is  there  any  truth  in  Lep- 
kowski's^  observation  that  whereas  front  teeth  have 
usually  one  bundle  of  blood  vessels,  back  teeth 
possess  two  or  more  bundles?  Let  the  student 
examine  the  developing  molars  of  the  elephant,  and 
many  of  the  larger  animals,  and  he  will  clearly  see 
an  apparent  fusion  of  simple  cone-shaped  bodies 
which  go  to  form  the  teeth.  The  molar  teeth  of  the 
mastodon  or  the  mammoth  exhibit  in  their  youngest  portions  a  con- 
glomeration of  a  few  cones.     (See  also  Fig.  315.) 

As  a  latter-day  teacher  of  this  theory  as  to  the  complex  pattern  of 
the  mammalian  crowns,  one  must  refer  to  the  works  of  Marett  Tims." 
He  has  shown,  first,  that  in  the  fishes  there  is,  in  certain  cases — as 
in  the  mud-fish  (Ceratodus) — a  fusion  of  individual  cusps;  secondly, 
amongst  the  reptiles  there  are  evidences  of  a  concrescence  in  the  devel- 
opment of  the  teeth  of  Sphenodon.  This  concrescence  theory  implies, 
therefore,  a  fusion  of  reptilian  cones,  which  give  rise  to  the  various 
cusps  of  the  mammalian  molars.  JMarett  Tims  adopts  this  theory 
as  far  as  it  relates  to  the  anterior  position  of  teeth  of  the  same  den- 
tition in  the  true  molar  region  only.  He  has  never  seen  fusion  of 
mammalian  enamel  organs.  He  has  noticed  a  striking"  numerical 
relationship  between  the  cusps  of  mammalian  teeth  and  the  number 
of  individual  teeth. 


Radiograph  of  two 
supernumerary  incis- 
ors, above  and  below 
an  unerupted  maxil- 
lary first  right  incisor. 


138  THE  EVOLUTION  OF   THE  MAMMALIAX  CROWNS 

Regarding  the  premolars,  the  base  of  the  reptihan  cone  is  surrounded 
by  a  cingulum,  which  has  already  been  mentioned.  In  process  of  evolu- 
tion, the  external  part  of  the  cingulum  disappears,  the  ends  of  the 
internal  cingulum  give  rise  to  small  anterior  and  posterior  cusps.  In 
this  way,  what  is  called  a  triconodont  tooth  is  formed.  An  examina- 
tion of  the  jaws  of  the  hyaena  and  the  cat  shows  this  beautifully,  the 
upper  third  premolar  in  each  case  presenting  obviously  a  three-cusped 
tooth.  These  cusps  increase  in  size,  and  the  premolars  are  very  pro- 
nounced, both  in  the  cat  and  in  the  hyeena.  The  fourth  upper  premolar 
is  a  very  large  tooth,  namely,  the  "carnassial"  tooth,  as  already  men- 
tioned. Marett  Tims  believes  that  the  origin  of  these  anterior  and 
posterior  cusps,  which  are  merely  an  elevation  of  the  ends  of  the  internal 
cingula,  may  be  due  to  mechanical  agencies.  Regarding  the  molars, 
he  considers  that  the  complexity  of  the  pattern  of  the  crowns  is  chiefly 
due  to  longitudinal  fusion  of  primitive  haplodont  cones. 

The  cingulum  of  the  dog  shows  an  elevation  into  cusps  in  the  incisors, 
premolars,  and  molars. 

THE    TRITUBERCULAR    THEORY* 

This  theory  holds  that  haplodont  teeth  have  cusps  developed  upon 
them.  From  America  came  its  origin.  Cope^  and  Osborn"  are  the 
great  exponents  of  it.  They  found,  in  a  fossil  jaw  of  a  small  extinct 
mammal,  certain  primitive  haplodont  cone-shaped  teeth  of  a  reptilian 
pattern.  This  was  the  Dromotherium  [o;io(/.oa7o^  =  running,  dvjf)  =  wild 
beast  ("the  running  animal")],  and  the  tooth  consisted  of  one  main 
cone  with  minute  lateral  cusps  upon  it,  the  root  being  grooved.  Here 
was  evidence,  to  their  mind,  of  the  first  stage  of  this  Tritubercular 
theory,  namely,  one  main  cone,  with  minute  lateral  cusps  upon  it. 
In  order  to  distinguish  this  principal  cone  from  others,  it  was  called 
the  protocone  {jipcoro:;  =  first). 

The  second  stage  of  the  theory  depended  upon  the  development 
upon  this  primitive  cone,  of  anterior  and  posterior  cusps.     This  con- 

*  This  term  is  inaccurate,  as  pointed  out  by  Beddard  ("Mammalia,  "  Cambridge  Natural  History, 
1902,  vol.  x),  "for  the  holders  of  this  view  do  not  derive  the  mammalian  molar  from  a  trituberculate 
condition,  but  in  the  first  place  from  a  simple  cone,  such  as  that  of  a  crocodile. " 


THE   TRITUBERCULAR   THEORY  139 

stituted  what  is  called  the  Triconodont  stage,  and  is  exemplified  in 
the  jaw  of  the  ancient  mesozoic  mammal,  the  Amphilestes  [Xnas-h^oTr,: 
("the  robber")].  Here  was  a  crown  elongated  in  an  anterior  and 
posterior  direction,  consisting  of  one  central  cusp  and  two  lateral  cones, 
the  root  being  bifurcated.  The  cone  in  front  of  the  main  cone  or  cusp 
(protocone),  was  called  the  paracone,  the  posterior  cone  was  called 
the  metacone.  Therefore,  from  before  backward,  the  three  cones 
were  known  as  para-,  proto-,  and  meta-  ("before,"  "First  or  prin- 
cipal," and  "behind").  Examples  of  these  triconodont  teeth  may 
be  seen  in  the  cheek  teeth  of  the  leopard-seal  at  the  present  day. 


ABC  D 

The  stages  of  trituberculism.  (After  Osborn.)  A,  hypothetical  pattern  of  haplodont  type, 
unknown  as  yet  in  primitive  mammals.  B,  protodont  type,  the  main  cusp  (protocone),  having  in 
front  the  paracone  and  behind  the  metacone,  exemplified  in  the  Dromotherium.  C,  triconodont 
type,  the  three  cusps  are  more  equal  in  size,  exemplified  in  Phascolotherium ,  and  the  leopard  seal. 
D,  tritubercular  type,  the  crown  being  triangular,  exemplified  in  Spalacotherium. 

The  third  stage,  or  the  Tritubercular  stage,  is  exemplified  in  the 
molar  teeth  of  the  Spalacotherium  {o-alat  =  a  mole).  This  Tricon- 
odont tooth  was  not  elongated  in  an  anteroposterior  direction,  but 
modified  into  a  triangular  form,  that  is  to  say,  the  anterior  and  pos- 
terior cones,  instead  of  being  in  a  straight  line  with  the  protocone, 
had  been  placed  to  the  side,  and  the  three  cusps  or  cones  were  thus 
arranged  in  a  triangular  form.  The  molar  teeth  of  the  mammals  of 
the  present  day  exhibit  this  Tritubercular  condition.  Osborn*  believed 
that,  in  the  evolution  of  countless  ages,  the  lateral  dental  cones  of 
creatures  like  the  lemurs,  rotated  inward  in  the  mandible,  outward 
in  the  maxilla.  In  each  case  the  protocone  formed  the  apex  of  the 
triangle.  In  the  upper  jaw  it  is  on  the  lingual  side;  and  in  the  lower 
jaw  it  is  on  the  labial  side. 

This  is  the  theory.  What  support  is  there  for  it?  Only  the  existence 
of  the  lower  molar  of  this  Spalacotheriiiui,   which   was  a  marsupial. 


140  THE  EVOLUTION  OF  THE  MAMMALIAN  CROWNS 

whose  remains  are  extremely  old,  and  whose  jaw  from  which  these 
deductions  were  made,  was  perhaps  only  one  and  one-half  inches  in 
length.  The  Tritubercular  theory  is  probably  correct  as  to  the  evolu- 
tion of  the  three  main  cusps;  but  the  chief  objection  lies  in  the  absence 
of  embryological  details,  and  the  entire  want  of  evidence  to  show  that 
rotation  of  cusps  takes  place. 

Investigating  the  evolution  of  the  molars  of  Man,  these  two  American 
observers  name  the  various  cusps  appearing  on  the  crowns  in  con- 
formity with  their  ideas  regarding  the  Tritubercular  theory.  Two 
illustrations  may  be  given  as  to  the  results  of  their  work.  Considering 
the  first  maxillary  molar  on  the  right  side,  which  is  a  four-cusped 
tooth,  fairly  quadrilateral  in  shape  in  a  typical  specimen,  the  anterior 
internal  cusp  is  the  most  prominent  and  marked.  This  is  the  protocone, 
and  it  corresponds  to  the  apex  of  the  primitive  triangle  or  "trigon" 
of  Qsborn.  It  is  connected  by  means  of  a  ridge  with  the  posterior 
external  cusp  which  corresponds  to  the  metacone  of  the  Trituberculists. 
The  anterior  external  cusp  is  the  paracone,  and  in  the  three  cusps  there 
is  the  primitive  triangular  form,  the  protocone,  as  has  already  been 
said,  being  the  apex  and  looking  inward  toward  the  palate,  the  para- 
cone forming  the  anterior  angle,  and  the  metacone  forming  the  posterior 
angle.  But  in  addition  to  these  three,  a  fourth  cusp  is  observable, 
occupying  a  posterior  internal  position.  This  is  termed,  by  Cope  and 
Osborn,  the  hypocone,  which  is  not  represented  in  the  original  triangle, 
but  means  the  "Cone  beyond"  the  original  triangle. 

Passing  on  to  the  first  mandibular  molar  on  the  right  side,  it  is 
seen,  in  a  well-formed  tooth,  that  five  cusps  are  represented  on  the 
occlusal  surface  of  the  crown,  two  anteriorly,  two  posteriorly,  and  one 
intermediate  between  the  two  posterior  cusps.  These  may  be  termed 
respectively,  the  antero-external,  the  antero-internal,  the  postero- 
external, the  postero-internal,  and  the  postero-median,  or  intermediate 
cusp.  The  application  of  the  Tritubercular  theory  to  this  tooth  is 
not  so  easily  accomplished  as  in  the  upper  molar,  but  acting  on  the 
assumption  of  the  apex  of  the  triangle  occupying  the  labial  side  in  the 
lower  jaw,  the  protocone,  therefore,  corresponds  to  the  antero-external 
cusp.  Be  it  noted,  however,  that  in  the  mandible  the  suffix  "id"  is 
applied  to  the  word  cone  to  distinguish  it  from  the  upper  jaw,  so  one 


THE  TRITUBERCULAR   THEORY 


141 


speaks  of  the  antero-external  cusp  as  the  protocouid.  The  puraconid, 
apparently,  cannot  be  accounted  for  in  this  first  right  lower  molar 
tooth.  The  metaconid,  however,  remains,  and  can  be  identified  with 
the  antero-internal  cusp,  while  the  hypoconid  is  represented  by  the 
postero-external  cusp.  The  postero-internal  cusp  is  known  as  the 
entoconid,  and  the  postero-median  is  known  as  the  hypoconuUd. 

The  probable  order  of  the  appearances  of  the  cusps  of  the  molars 
from  a  histological  point  of  view  is  as.  follow: 


Primates 
1st.    Paracone 
2d.    Protocone 
3d.    Metacone 
4th.  Hypocone 


1st.  Protoconid 
2d.  Metaconid 
3d.  Hypoconid 
4th.  Entoconid 
5th.  HypoconuUd 


Maxill.4 

Marsupials 
1st.    Paracone 
2d.    Protocone 
3d.    Metacone 
4th.  Hypocone 

Mandible 

1st.    Protoconid 
2d.     Paraconid 
3d.    Hypoconid 
4th.  Entoconid 
5th.  Metaconid 


Ungulates 
1st.    Paracone 
2d.     Metacone 
3d.     Protocone 
4tli.  Hj^pocone 


1st.  Protoconid 
2d.  Metaconid 
3d.  Hypoconid 
4th.  Entoconid 


The  foregoing  is  a  fair  statement  of  the  observations  of  Cope  and 
Osborn.  The  reader  is  referred  to  their  works  and  those  of  other 
observers  for  fuller  accounts. 

In  attempting  to  apply  the  cone  theory-  to  the  incisors,  the  canines, 
and  the  premolars,  one  may  point  out  that  the  incisor  may  have  been 
deri\'ed  from  a  cone  which  had  a  flattened  base,  flattened  in  an  antero- 
posterior direction  to  make  the  incisive  edge.  In  the  canine,  the  base 
is  transformed  into  a  trihedral  cone-like  prism.  In  the  premolars, 
at  first  sight  there  is  a  probable  fusion  of  two  cones  with  rounded  bases.  ^- 
Examination  of  a  typical  first  maxillarj-  premolar  shows  apparently 
a  duality  of  cones,  of  which  the  larger  is  on  the  outer  (buccal)  side. 
The  union  of  the  two  is  incomplete  as  in  the  second  premolar.  It  is 
difificult,  however,  to  consider  this  as  an  example  of  fusion  of  two  cones, 
on  account  of  their  relative  positions.  The}-  are  placed  laterally, 
and  never  occur  in  the  antero-posterior  diameter  of  the  tooth.  This 
lateral  position  would  presuppose  that  (i)  there  is  fusion  by  two  cones 
of  dissimilar  dentitions  of  which  the  buccal  would  represent  the  older, 


142  THE  EVOLUTION  OF  THE  MAMMALIAN  CROWNS 

and  the  lingual  the  younger  of  the  two,  viz.,  the  permanent  and  the 
post-permanent  types,  and  {ii)  that  both  dentitions  were  equally 
evolved.  While  there  is  no  obvious  dissimilarity  in  size,  it  is  conceiv- 
able that  an  undue  elevation  of  the  internal  portion  of  the  cingulum 
of  the  protocone,  represented  by  the  outer  cusp,  probably  explains 
the  prominence  of  the  lingual  cusp  of  the  tooth.  The  other  anterior 
teeth — incisors  and  canines — often  exhibit  a  small  cusp  on  the  lingual 
surface  which  is  evidently  the  elevated  cingulum  of  the  typical  tooth. 
This  theory  of  Trituberculism,  as  propounded  by  Cope  and  Osborn, 
has  been  controverted  by  many  people. 


'^W 

^:-^ 


The  crown  of  the  first  right  and  left  maxillary  molars,  showing  the  homologies  of  their  cusps. 
X  -f.     FT,  protocone;  FA,  paracone;  M,  metacone;  H,  hypocone. 

Fig.  82 


The  crowns  of  the  first  and  second  right  and  left  mandibular  molars,  showing  the  homologies  of  their 
cusps.     X  X-    P^'  protoconid;  H,  hypoconid;  HD,  hypoconulid;  £,  entoconid;  M,  metaconid. 

Objections  to  the  Tritubercular  Theory. — A  recent  writer — Wortman'*^ 
— who  has  studied  the  question  very  considerably,  advances  an  idea 
which  seems  more  plausible  than  the  above.  The  Carnivora  today 
are  derived  from  three  ancient  sub-orders:  (i)  The  Creodonta;  (2) 
the   Carnivora   or    the     Carnassedenta;    (3)    the    Pinnipedia.      In   the 


THE   TRITUBERCULAR   THEORY  143 

Creodonta,  the  carnassial  tooth  may  be  absent  or  present;  when  present, 
it  is  not  always  the  fourth  upper  premolar  and  first  lower  molar.  There 
is  no  living  representative  of  the  Creodonta  today,  but  their  fossil  bones 
have  been  discovered  in  the  Eocene  strata  in  Wyoming  and  Utah, 
and  also  in  New  Mexico.  Among  the  Creodonta  were  the  animals 
Dissacus  and  the  Mesonix.  In  these,  the  lower  molars  have  lost 
the  internal  cusp  of  the  triangle,  that  is,  the  protocone.  The  pattern 
of  the  teeth  thus  assumes  a  simple  premolar-like  shape.  This  is  not 
a  degenerative  change.  But  the  upper  teeth  are  of  great  importance. 
In  Dissacus,  the  first  and  second  premolars  have  simple  crowns  and 
one  small  posterior  heel.  The  third  premolar  shows  a  transitional 
stage,  a  second  heel  developing  on  the  lingual  side  of  the  principal 
cusp.  The  fourth  premolar  is  the  same,  but  still  more  advanced, 
namely,  the  tooth  consists  of  a  principal  cusp,  a  heel  or  posterior 
external  cusp,  a  lingual  cusp,  and  a  small  posterior  intermediate  cusp. 
In  the  first  upper  molar,  the  tooth  crown  is  nearly  triangular,  because 
of  the  increase  of  the  size  of  the  postero-external  and  the  longitudinal 
cusps,  but  the  antero-external  cusp  is  still  the  larger.  The  second 
molar  shows  a  state  of  development  intermediate  between  the  fourth 
premolar  and  the  first  molar.  In  Mesonix,  the  first  and  second  pre- 
molars, little  change  from  the  simple  type  was  noticed;  the  third 
premolar  had  a  postero-external  cusp  or  heel,  and  no  internal  cusp, 
but  the  heel  was  increased  in  size  till  it  and  the  principal  cusp  were 
equal.  In  the  fourth  molar  the  postero-external  cusp  has  increased 
in  size  till  both  are  equal,  and  the  internal  cusp  has  increased  in  size, 
making  the  tooth  look  like  a  molar.  The  first  and  second  molars 
are  very  similar. 

Now  take  a  single  cone-shaped  premolar  and  follow  it  through  many 
series  of  jaws  of  ancient  mammals,  and  the  result  of  one's  study  shows 
that  certain  new  cusps  come  to  be  added  in  a  different  way.  Thus, 
first,  a  cusp  is  added  to  the  posterior  border  as  a  basal  heel;  secondly, 
an  internal  cusp  arises  from  the  cingulum  and  becomes  the  main  internal 
cusp  of  the  tritubercular  crown.  The  exact  order  of  appearance  is, 
however,  not  constant.  But  Scott"  has  shown  that  the  tritubercular 
crown  of  every  complicated  premolar  thus  far  known  among  placental 
mammals  has  originated  by  the  addition  of  these  two  cusps  in  these 


144  THE  EVOLUTION  OF  THE  MAMMALIAN  CROWNS 

situations,  having  in  every  case  the  primitive  cusp  at  the  anterior- 
external  angle,  and,  therefore,  he  calls  these  the  protocone,  the  tri- 
cone,  and  the  dentary  cone  on   the  lingual  side. 

Now,  Wortman  believes,  and  his  theory  seems  more  likely  to  be 
correct,  that  as  there  is  so  much  similarity  in  the  fourth  premolar 
and  the  molars  of  Dissacus,  there  is  no  doubt  that  the  postero-external 
and  internal  cusps  have  been  added  to  the  protocone  and  the  original 
molars  in  exactly  the  same  manner  and  precisely  the  same  order  as 
they  have  been  in  the  premolars  as  seen  in  Mesonix,  and,  therefore, 
Osborn's  "rotation"  theory  is  wrong. 

To  conclude,  a  summary  of  what  has  already  been  given  may  be 
added.  The  Fusionists  believe  in  the  fusion  of  several  simple  cones, 
as  in  the  reptiles;  the  Trituberculists — of  whom  Osborn  believes  in 
rotation  of  cusps  and  Wortman  no  rotation,  but  mere  addition  of 
cusps — find  that  in  fossil  mammals  the  simple  cone  had  cusps  added 
to  it. 

As  has  already  been  stated,  there  is  a  constant  succession  of  teeth 
in  fishes  and  reptiles;  there  can  be  little  doubt  that  the  milk  and  per- 
manent teeth  of  mammals  represent  a  part,  at  least,  of  the  successive 
series  of  reptilian  teeth.  Much  discussion  has  taken  place  as  to  which 
of  the  two  dentitions  is  the  primary  in  mammals.  The  deciduous 
dentition  is  the  first  in  mammals,  generally;  but  in  marsupials  it 
appears  to  be  absent.  The  truth  probably  is  that  it  is  rudimentarj- 
in  Marsupialia.  Some  believe  that  in  Man  there  may  be  a  pre-milk 
and  post-permanent  dentition.  Vertical  sections  of  human  jaws 
show  occasionally  a  budding  out  from  the  tooth  band  on  the  labial 
side  and  a  budding  out  from  the  tooth  band  on  the  lingual  side,  in 
addition  to  the  presence  of  milk  and  permanent  tooth  germs.  Some 
believe  that  there  are  evidences,  therefore,  that  there  are  four  denti- 
tions in  such  a  section;  that  on  the  labial  side  being  the  pre-milk, 
that  on  the  lingual  side  the  post-permanent  enamel  germs.  Sufficient 
data,  however,  are  not  forthcoming  on  the  subject,  and  until  it  can 
be  proved  that  these  accessory  buddings  from  the  tooth  band  are 
true  enamel  organs,  and  are  about  to  produce  enamel,  it  is  impossible 
to  state  clearly  that  these  evidences  of  extra  dentitions  are  present  in 
Man.     If  it  were  so,  of  course,   it  would   represent  a  reversion  to  a 


THE   TRITUBERCULAR    THEORY  145 

reptilian  dentition,  and  taken  in  conjunction  with  tlie  characters  by 
supernumerary  and  supplemental  teeth,  tend  to  prove  a  mammalian 
descent  from  reptilian  progenitors. 

In  addition,  the  interested  reader  should  consult  the  writings  of 
Adloff,^  Ameghino,-  Rj'der,'"  and  Topinard.^^ 

References 

1.  Adloff.  "Einige  Besonderheiten  des  Menschlichen  Gebisses  und  ihre  Stammesgeschichtliche 
Bedeutung,  "  Zeitschrift  fiir  Morphologic  und  Anthropologie,  1906. 

2.  Ameghino.  "Sur  revolution  des  Dent  des  Mammiferes,"  Bol.  Acad.  Nat.  Ciencias  en  Cordova, 
1894;  "On  the  Primitive  Type  of  the  Plexodont  Molars  of  Mammals,"  Proc.  Zool.  Soc,  Lond.,  1899. 

3.  Cope.  "The  Mechanical  Causes  of  the  Origin  of  the  Dentition  of  the  Rodents,"  American 
Naturalist,  1888,  vol.  xxii.  "The  Mechanical  Origin  of  the  Sectorial  Teeth  of  the  Carnivora, " 
Proc.  American  Association  for  the  Advancement  of  Science,  1887.  "The  Tritubercular  Molar  in 
Human  Dentition,"  Journal  of  Morphology,  1888.  "The  Mechanical  Causes  of  the  Development 
of  Hard  Parts  in  Mammals,"  Journal  of  Morphology,  1889,  vol.  iii. 

4.  Kiikenthal.     " Znr  Dentitionira.ge,"  Anatomisch.  Anzeiger,  1895. 

5.  Lepkowski.  "Die  Verteilung  der  Gefasse  in  den  Zahnen  des  Menschen,"  Anatomische  Hefte, 
1901. 

6.  Forsyth,  Major.  "On  Some  Miocene  Squirrels,  with  Remarks  on  the  Dentition  and  Classifi- 
cation of  the  Sciurince,"  Proc.  Zool.  Soc.  London,  1893. 

7.  Marett  Tims.  "On  the  Origin  of  the  Mammalian  Teeth,"  Trans.  Odonto.  Soc,  1896,  vol. 
xxviii.  "On  the  Succession  and  Homologies  of  the  Molar  and  Premolar  Teeth  in  the  Mammalia," 
Journal  Anatomy  and  Physiology,  1902,  vol.  xxxvi.  "Evolution  of  the  Teeth  in  the  Mammalia," 
Journal  Anatomy  and  Physiology,  1903,  vol.  xxxvii. 

8.  Osborn.  "Evolution  of  the  Mammalian  Molars  to  and  from  the  Tritubercular  Type," 
Amer.  Naturalist,  1888.  "Recent  Researches  upon  the  Succession  of  the  Teeth  in  Mammals," 
American  Naturalist,  1893.  "Rise  of  the  Mammalia  in  North  America,  "  Proc.  American  Associa- 
tion for  the  Advancement  of  Science,  T.&t)2,.  "  The  History  of  the  Cusps  of  the  Human  Molar  Teeth,  " 
Journ.  Brit.  Dent.  Assoc,  1895.  "On  the  Structure  and  Classification  of  the  Mesozoic  Mammalia,  " 
Journ.  Academy  of  Natural  Sciences,  Philadelphia,  vol.  ix. 

9.  Rose,  C.  "Phylogenese  des  Saugetiergebisses, "  Biolog.  Centralblatt,  Band  xii.  "  Ueber 
die  Entstehung  und  Formabanderungen  der  Menschlichen  Molaren,"  Anatom.  Anzeiger,  1892, 
Band  vii. 

10.  Ryder.  "On  the  Mechanical  Genesis  of  Tooth  Forms,"  Proc.  Academy  Natural  Sciences, 
Philadelphia,  1878  and  1879. 

11.  Scott.  "The  Evolution  of  the  Premolar  Teeth  in  the  MammaUa, "  Proc.  Academy  Natural 
Sciences,  Philadelphia,  1892. 

12.  Thompson,  A.  Howard.     "A  Manual  of  Comparative  Dental  Anatomy,"  1899. 

13.  Topinard.  "De  I'Evolution  des  Molaires  et  Premolaires  chez  les  Primates  et  en  particulier 
chez  I'Homme, "  L' Anthropologie,  1892,  No.  1. 

14.  Virchow.  "Retention,  Heterotypic  und  Ueberzahl  von  Zahnen,"  Verhandf.  d.  Berliner  aiith- 
ropol.  Gesellschaft,  1886. 

15.  Woodward.  "On  the  Succession  and  Genesis  of  Mammalian  Teeth,"  Science  Progress,  1894, 
Band  i. 

16.  Wortman.  "The  Comparative  Anatomy  of  the  Teeth  of  the  Vertebrata,"  .-Imer.  System 
of  Dentistry,  1886.  vol.  i. 


CHAPTER    IX 
THE   TEETH    OF   THE    PRIMATES 

Introductory.— The  Teeth  of  the  Lemurs  and  the  Anthropoid  Apes.— Prehistoric  Man.— Rules 
for  Descriptions  of  Mammalian  Dentitions. — The  Dental  Index.— The  Facial  Angle.— The 
Gnathic  Index. 

CLASS    I.      MAMMALIA 

Sub-class  II.     Eutheria 

The  process  of  evolution  has  reached  its  highest  degree  of  develop- 
ment in  the  class  of  vertebrates  called  Mammalia,  and  in  the  order 
Primates  {Primus  =  first,  phonetically  Pri-ma-tes). 

The  first  ordinal  group  of  Eutherian  Mammals  designated  Primates 
originall}^  by  Linnaeus,  is,  as  its  name  signifies,  the  first  of  all  the 
artificial  subdivisions  of  warm-blooded  animals  which  suckle  their 
young,  whence  the  name  mammalia  is  derived.  By  some  authorities^ 
it  is  placed  last  on  the  list.  For  present  purposes,  the  classifications 
of  Flower  and  Lydekker'  and  Beddard^  may  be  adopted.  A  survey 
of  these  sections  and  divisions  thus  shows,  at  a  glance,  the  position  of 
Man  with  regard  to  the  other  members  of  the  same  group,  and  the 
other  orders  of  Mammalia. 

The  members  of  this  order  may  be  defined  as  Mammals  which  are 
completely  hairy,  and  generally  arboreal,  possessing  on  all  four  limbs 
five  digits,  usually  provided  with  flat  nails,  the  terminal  phalanges 
expanded  and  flattened  at  the  terminations.  Plantigrade,  the  fore 
feet,  as  a  rule,  are  grasping  organs,  the  hind  feet  being  used  for  both 
grasping  and  walking.  The  mammee  are  thoracic  (except  in  the 
Aye-aye),  and  sometimes  are  placed  in  the  axillae.  The  orbits  and  the 
temporal  fossae  are  partly  separated  by  an  osseous  ridge.  Clavicles 
are  universally  found.  The  lunar  and  scaphoid  bones  are  separate. 
The  femur  has  two  trochanters.  The  stomach  is  a  simple  sac,  except 
in  the  sacred  apes  of  Asia.     A  large  caecum  is  invariably  present. 


TEETH  OF  LEMURS  AND  ANTHROPOID  APES  147 

The  main  reasons  why  Man  is  included  in  the  Monkeys  and  small 
family  of  Lemurs,  as  apart  from  other  Mammals,  lie  in  certain  ana- 
tomical features  which  are  common  to  all.  Thus,  in  all,  the  hand  is 
a  grasping  organ,  furnished,  except  in  some  few  instances,  with  five 
fingers.  The  thumb  is,  in  the  majority  of  cases,  opposable,  and  in 
the  five-toed  hind  foot,  the  thumb  (great  toe)  is  similarly  opposable, 
except  in  man.  A  second  distinctive  feature  is  that  the  bony  orbits 
of  the  eyes  are  surrounded  by  an  unbroken  osseous  rim.  Thirdh", 
certain  general  dental  characteristics  are  found,  except  in  the  marmoset 
monkeys,  and  consist  of  the  broadening  and  flattening  of  the  crowns 
of  the  molars,  which  are  surmounted  by  cusps  or  ridges,  form  three 
pairs  on  each  jaw,  are  always  more  complex  in  pattern  and  larger  in 
size  than  the  premolars,  and  are  admirably  adapted  for  the  mastica- 
tion of  fruits,  leaves,  and  vegetable  substances. 

The  Order  consists  of: 

Sub-order  I.     Aiithropoidea — Anthropoid  apes. 

Family      I.      Hominidcc,  comprising  one  genus  Homo,  and 

one  species  Homo  sapiens — MAN. 
Family     II.     Simiidce — Man-like  apes. 
Family  III.     Cercopithecidce — Old-world  monkeys. 
Family  IV.     Cebidce — ^American  monkeys. 
Family     V.      Hapalidce — Marmosets. 

Sub-order  II.     Lemiiroidea — Lemurs. 


TEETH  OF  LEMURS  AND  ANTHROPOID  APES 

Of  these,  the  Lemurs  {Lemur — a  ghost)  are  of  the  lowest  type. 
Natives  of  Madagascar,  and  of  nocturnal  habits,  they  may  be  also 
found  in  Africa  and  the  southern  parts  of  Asia,  but  in  the  first-named 
locality  they  attain  their  maximum  development.  They  differ  from 
monkeys  in  that  they  have  longer  limbs,  smaller  fox-like  skulls,  and 
different  dentitions.  A  distinctive  character  of  this  group  is  the  fact 
that  the  second  toe  of  the  hind  foot  always  terminates  in  an  elongated 
curved  claw  or  talon. 


148  THE   TEETH  OF   THE  PRIMATES 

The  dentition  of  typical  lemurs  consists  of  two  pairs  of  maxillary 
incisors,  separated  from  one  another  by  a  considerable  gap  in  the 
middle  line,  and  four  slender  mandibular  procumbent  (horizontally 
placed)  incisors.  The  upper  canines  are  large.  The  lower  ones  small, 
like  incisors — and  there  is  some  doubt  about  their  homologies.  Hence, 
some  authorities"  call  these  teeth  third  incisors. 


Skull  of  a  typical  lemur.     X  *■     The  mandibular  third  premolar  performs  the  functions 

of  a  canine. 

Their  dental  formula  is:    I  |  C  y  Pm  I  M  |  x  2  =  36. 

The  most  aberrant  member  of  the  group  is  the  Aye-aye  {Cheiromys: 
xdji  =  hand ;  ,m^c  =  mouse) ,  an  arboreal  animal  which  mainly  eats  cater- 
pillars which  it  pulls  out  of  the  holes  of  trees  which  they  have  bored. 
Its  incisors  are  rodent-like  in  appearance  and  use,  for  they  are 
employed  in  gnawing  through  the  stems  of  the  sugar  cane. 

Its  formula  is:    I  |   C  |   Pm  ]r  M  |  x   2  =  18. 

The  American  monkeys  {Platyrrhini:  ~/«r'->c  =  broad ;  /''<:c=nose) 
include  ten  genera,  such  as  the  Howlers,  the  Capuchins,  the  Spider 
Monkeys,  the  Squirrel  Monkeys,  etc.,  and  differ  so  very  markedly 
from  the  Old  World  forms,  that  it  is  quite  possible  they  may  trace 
their  origin  from  an  altogether  independent  source,  and  if  the  anatomy 
of  their  teeth  is  to  be  depended  upon  for  information  upon  this 
point,  it  would  seem  as  if  their  origin  was  lower  and  less  specialized 
than  that  of  the  latter.     Thus,  they  possess  three  pairs  of  premolar 


TEETH  OF  LEMURS  AXD  AXTHROFOID  APES 


149 


teeth  in  each  jaw,  their  formula  being:  I  f  C  J-  Pm  4|  M  ;|  x  2  =  36. 
The  nostrils  are  widely  separated,  and  most  have  tails,  which,  when 
long,  are  frequently  prehensile.  The  thumb  is  non-opposable.  They 
inhabit  the  tropical  districts  of  Brazil.  The  marmosets  are  distin- 
guished dentally  in  that  they  have  only  two  pairs  of  molar  teeth  in 
each  jaw'. 

Fig.  84 


[Skeleton  of  a  New  World  monkey  (jV/;das).     X  J.    C/.  Figs.  92  and  93.    The  marmosets,  of  which 
this  is  a  photograph,  possess  only  four  pairs  of  molars  in  each  jaw. 

The  Old  World  monkeys  {Catarrhini:  /■<>'<'■  =  down  or  narrow,  ijk 
=  nose)  include  the  Orang-outang  of  Africa,  the  Gorilla  of  Africa, 
the  Gibbon  of  Borneo,  and  the  Chimpanzee  of  West  and  Central 
Africa.      Some    naturalists   place   amongst    the    Old    World    apes    the 


150 


THE   TEETH  OF   THE  PRIMATES 
Fig. 


B  C 

Skull  of  a  baboon  {Cynocephalus ,  or  Papio).     X  §.  The  crown  of  the  mandibular  first  premolar 

inclines  greatly  backwards.     A,  side  view;  B,  palate;  C,  mandible.     In  the  latter  supernumerary- 
molars  are  present. 


TEETH  OF  LEMURS  AND  ANTHROPOID  APES 


151 


Baboon  and  the  Mandril,''  of  Arabia  and  Africa.  These  differ  from 
the  former  by  their  mode  of  progression  "on  all  fours,"  by  having 
longer  legs  than  arms,  and  by  the  first  incisor  being  greater  than  the 
second  incisor. 

In  all,  the  dental  formula  is  the  same  as  in  Man:  If  CyPnif  M  |x2  =  32. 

/According  to  Professor  Lydekker,^  "These  dental  characters  afford 
very  important  evidence  of  the  close  kinship  of  the  man-like  apes 
to  Man  himself,  and  undoubtedly  outweigh  the  difference  in  the  form 


Skull  of  an  Old  World  male  monkey,  the  macague  {Macacus  rhesus).    X 


of  the  whole  dental  series  now  to  be  noticed,  which  is  largely  due  to 
adaptation.  In  both  the  upper  and  lower  jaws  of  Man  the  teeth  are 
arranged  in  a  regular  horse-shoe  series,  with  scarcely  any  interruption 
to  the  continuity,  by  the  tusks  which  are  but  little  taller  than  the 
other  members  of  the  series.  On  the  other  hand,  in  the  adults  (and 
especially  the  males  of  the  larger  species)  of  the  man-like  apes,  the 
cheek  teeth  are  arranged  in  a  nearly  straight  line,  and  form  a  more  or 
less  regulated  junction  with  the  line  of  the  incisors;  the  large  canines 
or  tusks,  occupying  the  angle  between  the  two  series,  and  thus  form- 
ing a  marked  break  in  continuity.  In  these  respects  the  man-like  apes 
resemble  their  inferior  kindred.  If,  however,  a  young  individual  of 
the  larger  man-like  apes,  and  especially  the  chimpanzee,  be  examined, 
it  will  be  found  that  the  teeth,  owing  partly  to  the  imperfect  protru- 


152  THE   TEETH  OF   THE  PRIMATES 

sion  of  the  tusks,  form  a  less  interrupted  and  more  regularly  curved 
series.  Indeed,  with  the  exception  that  the  whole  jaw  is  longer  and 
narrower,  and  the  partially  protruded  tusks  are  proportionately 
larger,  the  character  of  such  specimens  make  a  marked  approximation 
to  the  human  type,  and  the  jaw  of  a  chimpanzee  at  this  stage  may 
be  regarded  as  almost  intermediate  in  structure  between  that  of  Man 
and  that  of  an  adult  male  gorilla.  Moreover,  in  this  juvenile  state, 
the  long  union  of  the  two  branches  of  the  lower  jaw  partakes  of  the 
short  and  rounded  form  characterizing  that  of  Man;  whereas,  in  the 
adult  it  becomes  longer  and  more  deeply  channelled,  like  that  of  the 
lower  monkeys.  In  many  respects  the  teeth  and  jaws  of  the  gibbons, 
or  smallest  representatives  of  the  present  group,  conform  to  the  inter- 
mediate type." 

Other  features  of  the  man-like  apes  consist  in  their  having  very 
long  arms  compared  to  legs,  large  superciliary  ridges,  inclined  spinal 
columns,  broad  sternums,  and  no  tails.     (See  Figs.  97  and  98.) 

PREHISTORIC    MAN 

During  several  generations  the  mind  of  man  has  been  endeavour- 
ing to  trace  a  resemblance  between  human  beings  and  apes.  Many 
people  have  believed  in  the  existence  of  the  so-called  "missing  link," 
and  have  spent  much  time,  labour,  and  money  in  attempting  to  unravel 
the  mysteries  of  the  supposed  evolution  of  man  and  monkeys  from  a 
common  ancestral  type.  In  the  earlier  portion  of  last  century  it  was 
impious  to  distrust  the  Mosaic  story  of  Creation.  In  recent  times, 
however,  it  is  abundantly  clear  that  the  earth  is  much  more  ancient 
than  the  years  attributed  to  it  in  the  first  chapter  of  Genesis.  Science 
does  not  contravert  the  marvellous  narrative  as  there  recorded;  as  a 
matter  of  fact  it  agrees  from  the  point  of  view  of  the  order  of  Creation 
of  living  things,  but  it  discounts  the  accuracy  of  the  supposed  age  of 
the  Earth,  which  is  there  set  down  as  4000  B.C. 

Through  various  geological  periods  there  have  been  evidences  of 
Man's  existence  in  many  parts  of  the  world.  Preceding  the  historic 
age,  which  extends  back  probably  no  less  than  10,000  years  B.C.,  and 
dates  from  the  relics  of  the  earliest  Egyptian  burials,  such  as  those 


PREHISTORIC  MAN 


153 


Fig.  87 
FO/iMATTONS 


TYPES    OF     jvfji  j\r 


ALLUVIAL 
B  URIED 

CHANNEL 
•"■  THAJ^mS 

ZOWESr  TEE  RACE 

^^  GLACUL 

oO  ^  TERRACE 
3"'  GLACIAL 


100^  TERRACE 

BOULDER  CLAY 
2"-^  GLACIAL 
NID  GLACIAL 
CONTORTED  DRIFT 

CROMER  REDS 

NORWilCH  BEDS 
PLATEAU  Dili  IT 

J^-  GLACLAL 


RED 
CRAG 
SERLES 


CORALLINE 

CRAG 
SERIES 


A  geological  chart  showing  the  probable  sequence  of  strata  formed  in  England  during  the  recent 
Pleistocene  and  Pliocene  epochs.     (After  Professor  Keith.) 


154  THE  TEETH  OF   THE  PRIMATES 

exhibited  at  the  British  Museum,  come  the  Neohthic  and  Paleolithic 
ages,  or  Post-glacial  epoch.  Beyond  that  is  the  Pleistocene  or  Quater- 
nary period,  beyond  that  the  Tertiary,  which  includes  the  Pliocene, 
Miocene,  and  Eocene  formations,  which  cover  the  computed  number 
of  3,000,000  years.  In  the  latter — the  Eocene — the  relics  of  an  ancient 
type  of  lemur  have  been  found. 

The  Heidelberg  Jaw. — The  very  earliest  trace  of  fossil  man  yet 
discovered  in  Europe  is  that  of  the  jaw  of  the  Heidelberg  man.  Geolo- 
gists appear  to  be  agreed  that  this  relic  of  stupendous  age  was  laid 
down  in  a  stratum  formed  by  a  river  before  the  first  glacial  period 
settled  on  Europe.  The  sand-pit  where  it  was  discovered,  in  1908, 
is  situated  in  Baden,  close  to  Heidelberg,  in  the  valley  of  the  tributary 
of  the  river  Neckar.  Dr.  Schoetensack,  of  the  University  of  Heidel- 
berg, characterized  it  as  a  most  important  and  remarkable  find.  It 
was  possible,  he  conceded,  to  form  a  conception  of  the  stage  of  man's 
evolution  in  Europe  at  the  junction  of  the  Pliocene  and  the  Pleistocene 
periods.  The  main  features  of  the  jaw  were  the  massive  character 
of  the  long  framework,  which  at  first  sight  seemed  more  anthropoid 
than  human;  that  the  masticatory  muscles  must  have  been  more 
highly  developed  here  than  in  any  other  known  human  race;  that  the 
parts  were  ill  adapted  for  the  mechanism  of  speech;  that  the  mental 
eminence  represented  the  stage  in  the  evolution  of  the  chin  from  a 
Simian  condition.  It  was  apparent  that  only  a  very  primitive  stage 
in  the  evolution  of  language  had  been  reached.  This  jaw  is  believed 
to  have  been   1,000,000  years  old. 

The  Neanderthal  Skull. — Little  has  been  proved  by  the  discovery 
of  fragments  of  human  bones  found  in  various  countries  during  the 
last  century.  The  first  to  which  considerable  attention  was  attracted 
was  the  Neanderthal  skull,  unearthed  near  Diisseldorf  in  1856,  a  few 
years  before  the  publication  of  Darwin's  "Origin  of  Species."  The 
relic  showed  an  extremely  flattened  cranium  with  largely  developed 
superciliary  ridges.  Virchow  believed  it  to  be  that  of  a  deformed  type 
of  skull. 

Exploration  of  a  cave  in  the  cliffs  at  St.  Brelade's  Bay,  on  the  south 
coast  of  Jersey,  has  resulted  in  the  discovery  of  remains  of  the  very 
earliest  race  yet  known  in  Europe — the  Neanderthal. 


PREHISTORIC  MAN  155 

The  cave,  situated  60  feet  above  the  present  beach,  was  filled  and 
obscured  by  a  surface  fall  in  a  long  past  period,  but  in  more  recent 
times  has  become  exposed  by  the  action  of  the  sea.  The  exploration 
which  has  been  carried  out  by  the  Societe  Jersiaise,  was  suggested 
by  the  discovery  of  a  very  primitive  type  of  flint  implement  found 
in  the  rubble  below  the  site  of  the  cave,  Operations  were  begun  in 
1910,  and  when  the  floor  of  the  cave  was  reached,  after  the  removal 
of  25  feet  of  overlying  material,  extensive  traces  of  primitive  man 
were  found.  Old  hearths  were  indicated  by  the  fragments  of  char- 
coal and  burnt  earth,  numerous  flint  instruments  of  a  very  primitive 
type  were  found,  and  bones  and  teeth  of  certain  extinct  animals. 

The  bones  were  those  of  the  woolly  rhinoceros,  the  reindeer,  and 
two  varieties  of  horse.  The  teeth,  nine  in  number,  belonged  without 
doubt  to  an  individual  of  the  Neanderthal  race,  but  are  in  certain 
features  more  primitive  than  even  the  teeth  of  the  Heidelberg  mandible, 
usually  regarded  as  mentioned  above  as  the  earliest  remains  of  man 
yet  discovered  in  Europe  and  assigned  to  the  Glacial  period. 

This  is  the  first  discovery  of  Neanderthal  man  outside  the  limits 
of  the  Continent  of  Europe.  It  is  probable  that  Jersey  was  united 
with  the  mainland  when  it  was  inhabited  by  the  Neanderthal  type  of 
man. 

The  Man  of  Spy. — In  1886,  two  Belgian  professors,  Fraipont  and 
Lohest,  found  at  Spy  two  similar  skulls  accompanied  by  portions  of  a 
skeleton.  It  was  surmised  that  they  were  contemporaneous  with  pre- 
historic man,  while  the  cerebral  capacities  approached  more  closely 
that  of  modern  man  than  of  the  ape,  viz.,  1300  c.c.  In  exceptional 
instances  the  greatest  human  cerebral  capacities  {e.  g.,  in  the  cases  of 
Byron  and  Cuvier)  measured  1800  c.c,  the  mean  being  1500  c.c,  while 
the  lowest  as  represented  by  the  aborigines  of  Australia  was  1400  c.c. 
The  cerebral  capacity  of  the  skull  of  an  anthropoid  ape  never  exceeds 
600  c.c. 

In  the  Spy  skulls  the  third  molars  were  larger  than  the  second, 
and  these  than  the  first,  all  having  three  roots. 

The  Pithecanthropus  Erectus. — In  1891,  Dr.  Dubois  brought  to 
Europe,  from  Java,  the  skull  of  a  creature  belonging  to  a  type  which 
appears  to  be  intermediary  between  man  and  ape.     It  can  be  placed 


156  THE  TEETH  OF   THE  PRIMATES 

in  the  Pleistocene  period,  and  probably  was  approximately  the  same 
age  as  that  of  the  Heidelberg  jaw.  Some  months  after  finding  this 
skull,  two  enormous  molar  teeth,  and  a  presumably  human  femur, 
were  exhumed  at  a  distance  of  fifteen  metres  away  from  the  place  where 
the  skull  had  been  buried.  From  the  skull  and  the  femur  he  recon- 
structed a  kind  of  ape  which  was  exhibited  in  Paris  in  1900.  To  this 
he  gave  the  name  of  Pithecanthropus  erectus.-  '^  Anthropologists  are 
not  in  accord  as  to  whether  the  Dubois  discovery  was  a  degenerate 
human  type  or  superior  ape,  or  an  ancestor  of  man,  and  are  not  yet 
agreed  as  to  the  age  of  the  geological  stratum  in  which  the  bones  were 
lying.     It  may,  however,  be  placed  among  the  Siniiidce.^ 

The  Mousterian  Relics. — The  relics  of  a  human  being  were  found 
in  August,  1908,  in  a  cave  at  La  Chapelle-aux-Saints,  in  France,  which 
are  less  problematical  in  their  origin  than  those  already  mentioned. 
That  skull  and  another  found  in  March,  1908,  in  the  cave  of  Le 
Moustier,  were  decided — on  account  of  the  nature  of  the  geological 
strata  in  which  they  were  interred,  together  with  some  bones  of  the 
reindeer  and  bison  and  chip  flints — to  belong  approximately  to  the 
same  age  as  the  skulls  of  the  men  of  Neanderthal  and  Spy.  Of  the 
latter  (the  Mousterian  skull).  Professor  Reichardt,  of  Bale,  made  a 
minute  examination,  when  it  was  seen  that  the  cranium  was  dolicho- 
cephalic in  type  and  remarkable  for  the  thickness  of  the  bones,  and 
possessed  marked  superciliary  ridges;  that  the  forehead  receded;  and 
that  the  mandi'ble  was  prominent  and  without  a  mental  eminence 
and  of  extraordinary  strength. 

The  Galley  Hill  Man. — Quite  recently  a  most  fascinating  series  of 
lectures  on  "The  Fossil  Remains  of  Man"  has  been  delivered  b}' 
Professor  Arthur  Keith,  of  the  Royal  College  of  Surgeons,  of  England. 
He  described  the  earliest  known  remains  of  a  human  being  ever  found 
in  England,  which  was  discovered  in  the  undisturbed  upper  gravel 
"terrace"  of  the  Thames  Valley  at  Galley  Hill  near  Northfieet. 

The  approximate  antiquity  of  fossil  remains  is  arrived  at  by  com- 
puting that  1000  years  must  elapse  before  a  river  can  wear  down  its 
bed  the  depth  of  one  foot.  It  is  extremely  probable  that  the  bed  of  the 
Thames  has  been  lowered  and  raised  170  feet  since  the  upper  gravel 
"terrace"  was  deposited  in  Post-glacial  or  Neolithic  periods.     Hence, 


PREHISTORIC  MAN  157 

on  this  basis  of  computation  it  may  be  estimated  that  the  antiquity 
of  the  Galley  Hill  man  was  170,000  years.  It  is  amazing  to  think 
how  ancient  is  the  modern  type  of  man,  for  although  differing  in 
several  features,  it  is,  in  essence,  modern  in  type — another  proof  that 
evolution  works  exceedingly  slowly. 

Our  knowledge  of  the  physical  characters  of  the  inhabitants  of 
Great  Britain  began  with  the  examination  of  the  Gallej'  Hill  man,  as 
just  recorded. 

The  Ipswich  Man. — Since  then,  however,  October,  191 1,  another 
most  important  discovery  has  been  made.  This  was  that  of  a  Pre- 
Boulder  clay  man  in  Suffolk,  whose  skeleton  dates  back  to  the  begin- 
ning of  the  Glacial  age,  or  perhaps  even  an  earlier  period,  distant 
100,000  years  or  more. 

To  the  reader  this  extraordinary  revelation  is  of  peculiar  interest, 
as  two  dental  surgeons  were  called  in  among  other  experts  to  examine 
in  detail  the  remains  and  the  teeth.  The  skeleton  was  lying  on  its 
right  side,  the  arms  being  flexed  and  legs  folded  up  in  the  vertebral 
column — a  posture  not  unlike  that  adopted  for  burial  of  the  dead  in 
Neolithic  times.  He  was  a  tall  man,  nearly  six  feet  in  height,  and 
though  the  jaws  were  lost,  the  isolated  teeth  were  preserved  and 
found  to  be  small  in  size,  very  much  worn  down,  not  materialh'  differ- 
ent from  the  modern  type  of  tooth,  and  totally  dissimilar  to  those  of 
Neanderthal  man.  The  cranium  was  small  and  flat  and  broad  in 
the  occipital  region.  The  femora  were  the  same  as  obtains  in  Man 
today,  as  were  also  the  bones  of  the  forearms  and  hands.  The  tibia 
and  fibula,  however,  had  a  peculiar  shape,  and  at  once  distinguished 
this  skeleton  from  all  Neolithic  races  and  from  every  form  of  man 
yet  discovered. 

The  Tilbury  Skull. — The  next  oldest,  as  far  as  yet  ascertained,  is  the 
skull  of  an  individual  found  in  excavating  for  the  Tilbury  Docks  in 
1883,  which  is  probably  30,000  years  old. 

The  portions  of  this  cranium  were  found  imbedded  in  the  sands 
thirty-four  feet  below  the  surface  of  the  ground,  under  layers  of  mud, 
clay,  and  peat,  which  were  placed  alternately,  and  the  size  and  shape 
of  the  head  can  be  accepted  as  a  type  of  those  which  prevail  in  England 
today. 


158 


THE   TEETH  OF   THE  PRIMATES 


Other  Skulls. — Similar  crania  have  been  discovered ;  one  in  Derby- 
shire in  a  cave,  associated  with  the  bones  of  reindeer,  bear,  hyaena,  etc. — 


The  mandible  of  a  man  of  Britain,  dating  from  370  a.d.     X  *.    Viewed  from  the  right  side. 

Fig.  89 


The  mandible  of  a  man  of  Britain,  dating  from  370  a.d.     X  }-.     Viewed  from  the  left  side. 

mammals  long  ago  extinct;    one  in  the  Cheddar  Caves;   another  in 
a  tumulus  in  Anglesey;  and  finally,  the  almost  complete  skeleton  of  a 


PREHISTORIC  MAN 


159 


man  found  in  1910,  in  an  undisturbed  prehistoric  (Neolithic)  stratum, 
which  is  being  exposed  by  the  encroachments  of  the  sea  on  the  coast 
of  Essex,  near  Walton-on-the-Naze.       An  antiquity  of  at  least  4000 

Fig.  90 


The  same,  viewed  from  above.     X  l-    The  first  molar  had  undergone  severe  attrition. 

years  can  be  assigned  to  this  Englishman.  He  was  a  finely  made 
young  man,  with  a  stature  of  5  feet  2  inches,  sharp,  prominent  nose, 
and  finely  moulded  face.  There  was  distinct  evidence  of  a  specializa- 
tion in  the  right  arm,  pointing  to  a  trade.  His  teeth  were  worn  flat, 
and  met   edge  to  edge,    as   in    prehistoric  races.      He   evidently   died 


Fig.  91 


Two  premolars  and  two  molars  from  the  same,  showing  great  attrition.     X  ~. 


in  the  autumn,  for  within  the  skeleton  were  detected  over  a  pint  of 
seeds  of  the  blackberry  and  dog  rose,  indicating  the  form  of  diet  then 
available. 


160  THE   TEETH  OF   THE  PRIMATES 

To  come  to  modern  times  (circa  370  a.d.),  some  human  bones  were 
recently  found  in  a  tumulus  on  the  northeast  coast  of  Yorkshire,  about 
two  miles  southeast  of  Saltburn,  on  the  edge  of  a  cliff  about  five 
hundred  and  twenty  feet  above  sea  level.  The  tumulus  contained  a 
fortified  Roman  outpost,  and  in  the  centre  was  a  well,  thirteen  and 
a  half  feet  deep.  Seven  feet  from  the  top  of  the  well  the  explorers 
found  human  remains,  of  which  one  (reconstructed)  skull  has  been 
declared  by  Professor  Keith  to  be  unmistakably  British.  The  coins 
and  pottery  found,  assign  a  date  of  350-400  a.d.  The  remains  were 
all  placed  head  downwards.  From  a  dental  point  of  view  the  jaws 
and  teeth  are  interesting,  especially  as  their  age  is  specifically  that  of 
1540  years.  The  molars,  as  seen  in  the  photographs  (Figs.  90  and  91), 
exhibit  much  attrition  on  their  enamel  surfaces.  The  angles  and 
sigmoid  notches  of  the  mandible  vary  from  those  of  a  more  modern 
type.  Through  the  kindness  of  Mr.  Gerald  Marshall,  the  author  has 
been  enabled  to  examine  critically'  and  to  photograph  these  jaws. 


THE    PRESENT    POSITION    OF    THE   THEORY   OF    HUMAN 
EVOLUTION 

Professor  Keith  {British  Medical  Journal,  April  6,  1912)  writes 
as  follow: 

"All  the  evidence  indicates  a  very  great  antiquity  for  the  later 
phases  in  the  evolution  of  the  human  body.  More  than  forty  years 
ago  Sir  Charles  Lyell  expressed  his  belief  that  the  remains  of  man 
would  be  found  in  the  Cromer  beds  of  East  Anglia.  Although  the 
actual  bones  of  man  have  not  been  found  in  those  beds,  flints  worked 
by  man's  hands  have  been  discovered  not  only  in  the  Cromer  beds, 
but  also  beneath  a  deeper  and  much  older  formation — the  red  crag. 
Mr.  Reid  Moir,  the  discoverer  of  the  pre-crag  flints,  regards  them  as 
being  of  at  least  early  Pliocene  age.  The  eoliths  of  the  uplands  of 
Kent,  although  of  a  somewhat  later  date  than  the  pre-crag  flints, 
serve  better  to  convey  an  idea  of  the  time  which  has  elapsed  since  men 
first  lived  on  the  Kentish  plateau.     It  is  a  most  fortunate  circumstance 


PRESENT  POSITION  OF   THE   THEORY  OF  HUAIAN  EVOLUTION     161 

that  these  implements  were  first  observed,  and  their  antiquity  inferred 
by  the  late  Sir  Joseph  Prestwich — a  geologist  of  sound  judgment, 
and  conservative  in  his  estimates  as  regards  the  past  period  of  man. 
We  owe  much  to  Mr.  Benjamin  Harrison  for  the  manner  in  which 
he  has  developed  our  knowledge  of  these  early  flints.  The  deposit 
or  "drift"  in  which  the  crudely  worked  flints  or  eoliths  are  found  is 
mixed  with  fragments  of  greenstone  and  chert.  The  strata  from  which 
these  greenstone  fragments  have  been  washed  lie  now  in  the  weald 
five  hundred  feet  below  the  level  of  the  southern  edge  of  the  plateau. 
Prestwich  realized  that,  at  the  time  these  ancient  flint  implements 
.were  imbedded,  hills  containing  the  greenstone  strata  must  have 
occupied  the  position  of  the  weald,  and  towered  high  above  the  level 
of  the  Kent  plateau,  and  that  after  the  greenstone  fragments  and 
flint  implements  were  imbedded  on  the  plateau,  these  hills  had  been 
gradually  washed  away  to  a  depth  of  at  least  one  thousand  feet.  The 
lowlands  of  the  weald  have  thus  been  formed  since  Pliocene  man  cut 
the  implements  now  found  in  the  plateau  drift.  When  these  facts,  and 
the  existence  of  a  primitive  form  of  anthropoid  in  the  earlier  part  of 
the  Oligocene  period,  are  kept  in  mind,  it  becomes  possible  to  believe 
in  the  existence  of  Pliocene  man  of  a  modern  type — such  as  Professor 
Ragazzoni  had  discovered  in  the  north  of  Italy. 

"Another  consideration  made  anthropologists  claim  a  great  antiquity 
for  modern  man — in  contradistinction  to  Neanderthal  man.  Man- 
kind as  seen  in  the  world  today — European,  Mongolian,  Red  Indian, 
and  Australian — were  most  diverse  in  type.  Their  evolution  from  a 
common  form  demanded  the  elapse  of  an  enormous  length  of  time.  In 
England  we  find  the  types  of  skulls  of  her  most  ancient  inhabitants 
repeated  in  her  modern  population.  With  the  exception  of  the 
Neanderthal  type,  all  the  ancient  Continental  forms  are  still  to  be 
found  in  Europe.  From  predynastic  to  modern  times  Professor  Elliot 
Smith  found  that  the  skull  of  the  Egyptian  has  changed  only  in  detail. 
The  oldest  human  crania  found  in  America  are  of  the  Red  Indian 
type.  We  are  forced  to  believe  that  human  evolution  works  slowh-; 
yet  it  has  effected  the  extraordinary  contrast  seen  between  two  such 
representatives  of  the  modern  type  as  the  negro  of  Africa  and  the 
fair-haired   native  of   North    Europe.     To  accomplish   such   a  degree 


162  THE  TEETH  OF   THE  PRIMATES 

of  divergence  one  must  carry  the  history  of  modern  man  at  least  well 
within  the  Pliocene  period.  Of  the  survivals  of  ancient  human  forms, 
it  is  very  likely  that  the  aboriginal  Australian  is  the  best  living  repre- 
sentative of  Pliocene  man.  From  such  a  type  one  can.  understand  the 
origin  of  the  negro  on  the  one  hand,  and  of  the  European  on  the  other. 
Neanderthal  man  was  a  yet  earlier  and,  in  his  later  development,  a 
yet  more  aberrant  type. 

"Two  discoveries  made  in  recent  years  appear  to  render  it  impossible 
to  suppose  that  the  modern  type  of  man  existed  so  early  as  the  Pliocene 
period.  The  first  was  the  discovery  of  the  Heidelberg  jaw  in  a  stratum 
belonging  to  the  oldest  or  first  stage  of  the  Pleistocene  epoch.  It  was 
of  a  most  primitive,  brutal,  and  yet  human  character.  It  indicates 
an  individual  of  the  Neanderthal  type,  but  of  a  more  massive  form 
than  is  found  at  a  later  date  in  France.  If  we  accept  the  Heidelberg 
individual  as  typical  of  the  human  race  of  that  period  (early  Pleisto- 
cene), then  we  must  suppose  that  human  evolution  proceeded  at  a  more 
rapid  rate  than  we  have  at  present  any  conception  of.  We  have  to 
remember  that  in  the  world  today,  and  it  has  always  been  the  case, 
there  are  types  or  forms  representing  very  different  degrees  of  antiquity 
and  stages  of  evolution.  It  is,  therefore,  not  only  possible,  but  probable, 
that  the  Heidelberg  and  Neanderthal  man  are  survivals  of  a  very 
ancient  type,  and  in  no  way  indicative  of  the  stage  reached  by  Homo 
sapiens  in  the  Pleistocene  period.  Using  the  same  manner  of  reason- 
ing, it  is  unlikely  that  the  man  of  Java  {Pithecanthropus) ,  who  was 
very  little  older  in  date  than  the  Heidelberg  man,  and  had  a  brain 
capacity  of  only  about  half  that  of  modern  man,  represented  the  high- 
est type  of  man  of  his  time.  He,  too,  was  evidently  a  survival  of  an 
early  stage.  At  least,  it  is  difficult  to  believe  that  in  a  single  and  short 
geological  period,  even  allowing  that  the  extent  of  that  period  may  be 
a  million  years,  man  could,  even  in  that  space  of  time,  double  his 
brain  capacity.  No  parallel  instance  of  so  rapid  a  degree  of  evolution 
can  be  found  in  the  history  of  Pleistocene  mammals. 

"As  regards  the  degree  of  relationship  between  man  and  the  great 
anthropoids  the  opinion  of  scientific  men  has  changed  very  little  since 
Darwin's  time.  Huxley  regarded  the  structural  difference  between 
man  and  the  gorilla  as  about  equal  in  degree  to  that  which  separated 


PRESENT  POSITIOX  OF   THE   THEORY  OF  HUMAX  EVOLUTION     103 

the  gorilla  from  ordinary  monkeys.  The  divergence  between  the 
gorilla  and  monkey  is  undoubtedly  the  greater.  It  can  be  safely  said 
that  the  brain  of  the  gorilla  represents  an  intermediate  stage  between 
the  brains  of  man  and  of  the  small  anthropoid  (the  gibbon) ;  the  brain 
of  the  dog-like  monkeys  represents  a  still  lower  or  more  primitive 
stage.  In  1904,  Professor  Nuttall  confirmed  the  inferences  which 
anatomists  had  drawn  concerning  the  relationship  of  man  to  anthro- 
poids and  monkeys.  He  established  the  fact  that  the  blood  of  the 
great  anthropoids  reacts  to  certain  tests  in  almost  exactly  the  same 
manner  as  human  blood;  the  reaction  becomes  less  in  amount  when 
the  test  is  applied  to  the  blood  of  monkeys.  The  response  in  the  case 
of  those  of  the  Old  World  is  greater  than  with  those  of  the  New,  thus 
bearing  out  the  anatomists'  opinion  that  the  Old  World  monkeys  are 
more  recently  related  to  the  human  stock  than  those  of  South  America. 
There  is  also  the  evidence  of  disease.  The  great  anthropoids  are  sus- 
ceptible to  syphilis — a  human  disease;  monkeys  can  be  inoculated 
with  difficulty.  Anthropoids  in  captivity  frequently  are  liable  to 
typhoid  fever;  and,  when  kept  in  captivity,  frequently  die  from  that 
very  human  disease — appendicitis.  There  was  no  evidence  that 
appendicitis  occurred  when  the  anthropoids  lived  in  their  native  habitats 
and  on  their  natural  diet.  Anthropoids  are  manifestly  human  as 
regards  the  nature  of  their  diseases. 

"Although  none  of  the  existing  anthropoids  could  be  regarded  as 
a  human  ancestor,  there  could  be  no  doubt,  seeing  the  extraordinary 
degree  of  structural  similarity,  that  man  and  the  great  anthropoids 
were  the  products  of  a  common  stem.  The  gorilla  shows  the  nearest 
structural  approach  to  man.  (See  Figs.  92  and  93.)  As  to  the  time 
at  which  divergence  occurred  between  the  great  anthropoid  and  human 
lines  of  descent  no  definite  statement  can  as  yet  be  made,  but  to  obtain 
a  working  hypothesis  it  is  necessary  to  place  the  point  of  divergence  in 
a  comparatively  remote  geological  epoch — the  Oligocene.  The  evolution 
of  the  great  from  the  small  anthropoids  may  have  occurred  early  in 
the  same  period.  The  genealogical  trees  which  have  been  constructed 
to  explain  the  past  history  of  the  human  stock  are  as  yet  little  better 
than  crude  guesses  to  explain  masses  of  ascertained  facts  of  anatomy. 
Further  discoveries  will  certainly  cause  these  genealogical  trees  to  be 


164 


THE  TEETH  OF   THE  PRIMATES 


modified  in  detail,  yet  the  sequence  of  events  in  the  evolution  of  man's 
body  is  becoming   clear.     The  great  mass  of  his  brain  and  his  nude 

Fig.  92 


Skeletons  of  a  man  and  a  gorilla  {Gorilla  gorilla) 


Front  aspect. 


skin  were  evidently  the  latest  of  human  acquisitions;  the  adaptation 
of  the  lower  limbs  for  walking  and  the  modification  of  his  teeth  to 


PRESENT  POSITION  OF   THE   THEORY  OF  HUMAN  EVOLUTION     1G5 

their  present  form  were  earlier  modifications  of  his  structure.     The 
size  of  his  bod\-  and  his  stature  were  still  older  human  features,  while 


Fig.  93 


The  same;  side  aspect. 


the  chief  structural  modifications  to  adapt  the  body  to  an   upright 
or  vertical  posture,  were  of  very  ancient  origin." 


166  THE   TEETH  OF   THE  PRIMATES 


DESCRIPTIONS    OF    DENTITIONS 

In  describing  the  various  dentitions  of  Mammals  it  is  important 
to  divide  the  subject  into  the  consideration  of 

1.  The  position  of  the  teeth. 

2.  Their  number. 

3.  Their  shape. 

4.  Their  structure. 

5.  Their  implantation. 

6.  Their  succession. 

7.  The  shape,  movements,  and  articulations  of  the  jaws,  and 

8.  The  functions  of  the  teeth. 

If  the  above  be  applied  to  the  typical  Mammalian  placental  denti- 
tion, the  description  would  generally  read  as  follows: 

1.  Implanted  in  the  Premaxillary,  Maxillary,  and  Mandibular 

bones. 

2.  Dental  formula:  I  |  C  i  Pmf  M  |  x  2  =  44. 

3.  Heterodont. 

4.  Enamel,  orthodentine,  cementum. 

5.  Gomphosis. 

6.  Diphyodont,  or  rarely  monophyodont. 

7.  Variable  shapes  and  movements. 

8.  Various  functions. 

If  applied  to  the  anthropoid  apes,  as  follows: 

1.  Usual  position. 

2.  Dental  formula:   I  |  C  |  Pm  f  M  f  x  2  =  32. 

3.  Heterodont,  Megadont.     (Dental  Index  =  44). 

Caniniform  second  incisor,  diastema,  etc., 

4.  5,  and  6,  as  above. 

7.  Ginglymo-arthroidal  articulation. 

8.  Herbivorous  generally. 

The  Orang-outang  differs  from  Man  in  the  following  particulars: 

1.  The  absence  of  articulate  language, 

2.  The  feeble  type  of  its  intellectual  faculties,  which  are  far  below 

even  those  of  the  lowest  savages,  such  as  the  Papuans, 


DESCRIPTIONS  OF  DENTITIONS  167 

3.  The  stouter  body  and  more  prominent  abdomen, 

4.  The  coat  of  long  hair, 

5.  The  extremely  small  cranial  cavity,  and  ill-developed  brain, 

6.  Long  arms,  and  short  legs  with  prehensile  feet, 

7.  Flattened  nose  and  prolonged  nasal  septum, 

8.  Face  thrown  into  many  folds,  and  thick  pendulous  lips, 

9.  Jaws  prominent  (prognathous)  and  snout-like;  facial  angle, 

in  adults,  30  degrees;  and  the  mandible  incapable  of  lateral 
movements,  and 
10.   Its  dentition."     The  teeth  exhibit  very  well  the  transitional 
stages  in  types  of  pattern.     The  jaws  present  a.  {A)  Mega- 
dont  type  of  dentition,  the  Dental  Index  being  55.      Max- 
illary teeth:    First    incisors  are  large;  the  second  incisors 
caniniform;  canines  are    large;  first   premolars  are  canini- 
foi-m;  the  second  premolars  are  blunter,  both  having  three 
roots. 
Of  the  mandibular  teeth,  the  incisors  are  large,  canines  large, 
sexual,  and  late  in  eruption,    first  premolars  are  similar 
in  shape  to  canines,  but  have  shorter  and  blunter  crowns, 
the  second  premolars  possess  similar  cusps;  both  these 
teeth  have  two  roots. 
{B)  A  diastema  is  present. 

(C)  The  molars  increase  in  size  and  converge  at  the  back 

of  the  mouth. ^ 

( D)  There  is  a  square  dental  arch. 

(£)   Prognathism  is  marked,  the  Gnathic  Index  being  over 
103. 

It  is  unnecessary  to  detail  the  dentitions  of  the  other  anthropoid 
apes. 

Generally  speaking,  the  three  great  divisions  of  Mankind  differ 
in  the  standard  size  and  measurement  of  their  teeth.  White  races 
are  microdont,  that  is,  have  small  teeth.  Yellou',  or  Mongolian,  races 
have  a  mesodont  type  of  dentition,  and  Black  races,  which  include 
the  native  aboriginal  Australians,  a  megadont  dentition,  that  is,  they 
possess  large  teeth. 


168  THE   TEETH  OF   THE  PRIMATES 

It  has  been  commonly  held  that  colour  was  the  main  distinguish- 
ing feature  of  race.  This  is  probably  only  partially  true.  At  all  events, 
it  would  appear  that,  as  prehistoric  man  can  be  divided  into  six  dis- 
tinct racial  types,  this  division  can  be  carried  down  to  the  present 
time,  being  based  upon  facial  contour  and  cranial  morphology.  As 
in  the  so-called  Anglo-Saxon  period  there  are  six  types,  so  in  these 
modern  days.  It  is  possible  to  demonstrate  clearly,  from  the  two 
factors  named,  viz.,  cranial  shapes  and  facial  contours,  that  national 
heterogeneity  in  ethnic  composition  depends  upon  the  variations  of  six 
patterns.  These,  as  far  as  the  British  peoples  are  concerned,  may  be 
known  as  the  Celtic  (25.2  per  cent.)  square  faced;  Ligurian  (20.4  per 
cent.)  pentagonal  face;  Magian  (16. i  per  cent.)  round  face;  Iberian 
(14.4  per  cent.)  oval  face;  Remian  (12.2  per  cent.)  pointed,  oval  face; 
and  Teutonic  (11.4  per  cent.)  oblong  face." 

The  Microcephalic  races,  such  as  the  Native  Australians  and  the 
Andaman  Islanders,  possess  a  cranial  capacity  of  less  than  1350  cm., 
the  Mesocephalic,  Chinese  and  African  negroes,  from  1350  to  1450 
cm.,  and  the  Megacephalic,  Europeans,  Japanese,  Esquimaux — over 
1450  cm. 

A  certain  standard  of  measurement  must  be  adopted  in  determining 
these  differences,  by  which  the  sizes  of  the  teeth  can  be  ascertained  and 
measured  in  their  relation  to  the  dimensions  of  the  skull. 

Dental  Index. — What  is  known  as  the  Dental  Index  is  used  for  this 
purpose. 

The  Dental  Index  is  the  standard  of  measurement  of  the  relation 
of  the  size  of  the  teeth  to  the  dimensions  of  the  skull,  and  can  be  ascer- 
tained by  means  of  the  following  formula,  the  length  of  the  distances 
being  marked  out  by  the  help  of  specially  contrived  calipers. 

The  length  of  the  teeth  X  loo 
The  basio-nasal  line. 

The  "length  of  the  teeth"  means  the  distance  from  the  mesial  aspect 
of  the  first  premolar  and  the  distal  aspect  of  the  third  molar,  all 
in  situ;  the  basio-nasal  line  being  an  imaginary  line  drawn  from  a  spot 
in  the  middle  line  of  the  anterior  margin  of  the  foramen  magnum  of 
the  occipital  bone  (the  basion),  and  the  junction  of  the  nasal  bones,  with 


DESCRIPTIO.\S  OF  DE.\TrnOAS 


169 


the  nasal  process  of  the  frontal  in  the  centre  of  the  lower  edge  of  the 
nasal  notch. 

It  has  been  found  by  direct  measurement  of  jaws  and  skulls  that  the 
dental  indices  of  microdont,  such  as  the  British,  mesodont,  such  as 
the  Chinese,  and  megadont  races,  equal  respectively  42,  43,  and  44 
to  47.     In  the  orang-outang,  as  already  noted,  it  measures  55. 

A  diastema  means  a  space,  vis.,  the  space  existing  in  each  maxilla 
of  certain  members  of  the  higher  orders  of  Mammalia.  It  is  a  pro- 
vision on  the  part  of  Nature  for  the  accommodation  of  the  mandibular 
canine,  which,  in  occlusion,  on  account  of  its  length,  passes  in  front 
of  its  maxillary  namesake.  It  thus  intervenes  between  the  maxillarj- 
second  incisor  and  canine. 

Fig.  94 


The  palatal  aspect  of  the  maxillae  of  a  man  of  New  Guinea  showing  a  diastema  between  the 
second  incisors  and  the  canines.     From  a  photograph  by  Dr.  W.  H.  L.  Duckworth. 

In  human  skulls  it  is  absent,  as  a  rule,  but  it  may  exist.  Thus,  Dr. 
Duckworth'  has  described  diastemata  in  the  jaws  of  natives  of  New 
Guinea,  which  are  preserved  in  the  Museum  of  Cambridge  University 
(Fig.  94)- 

A  prognathous  animal  or  human  being  is  one  whose  upper  jaw 
projects  more  forward  than  is  usual.  The  lower  races  of  mankind 
exhibit  this  characteristic,  e.g.,  the  Australian  aborigines,  the  nati\es 


170 


THE   TEETH  OF   THE  PRIMATES 


of  certain  parts  of  Africa/  of  Sumatra,*  etc.,  and  approach  in  type  of 
countenance  the  chimpanzee  or  orang-outang. 

To  obtain  this  degree  of  prognathism  the  facial  angle  and  the  gnathic 
index  must  be  investigated. 


Fig.  95 


Skull  of  a  native  of  German  East  Africa.      X  f 

Cf.  Fig 


Showing  a  marked  degree  of  prognathism. 


*  A  people  without  any  form  of  religion,  without  superstition,  devoid  of  any  thought  of  the  future 
state,  has  been  found  in  the  interior  forests  of  Sumatra,  according  to  Dr.  Wilhelm  Valez,  the  geologist 
of  the  University  of  Breslau,  who  has  made  extensive  journeys  through  the  island.  There  he  found 
the  Kubus,  as  he  named  them,  who  are  scarcely  to  be  distinguished  from  the  small  man-Uke  ape  of 
the  Indo-Malayan  countries.  They  are  wanderers  through  the  forest  seeking  food.  They  have  no 
property.  They  are  not  hunters,  but  simply  collectors.  They  seek  merely  sufficient  nuts,  fruits, 
and  other  edible  growths  to  keep  them  alive. 

The  Kubus  wage  very  little  warfare  upon  the  small  amount  of  animal  life  in  their  silent  and  sombre 
land.  The  only  notion  Professor  Valez  could  get  from  them  of  a  difference  between  a  live  and  a 
dead  person  was  that  the  dead  do  not  breathe.  He  infers  that  they  are  immeasurably  inferior  to 
the  Paleolithic  man  of  Europe,  who  fashioned  tools  and  hunted  big  game  with  his  flint-tipped  arrow 
and  knife.  Intellectual  atrophy  is  the  result  of  the  Kubus'  environment.  The  words  they  know  are 
almost  as  few  as  the  ideas  they  try  to  express. 


DESCRIPTIONS  OF  DENTITIONS 


171 


Facial   Angle. — The   Facial    angle*   is   an    angle   contained    between 
two  imaginary  lines,  one  drawn  from  the  most  prominent  part  of  the 


Fig.  96 


Fig.  97 


Fig.  98 


C— 


The  facial  angles  of  (^ )  a  dog,  (B)  a  monkey-,  and  (C)  a  European  man,  all  drawn  to  the  same 
scale.     A ,  the  incisive  point ;  C  A,  the  basio-alveolar  line. 


172 


THE  TEETH  OF   THE  PRIMATES 


forehead  to  the  prosthion  or  "alveolar  point,"  that  is,  the  point  in 
the  upper  jaw  which  lies  on  the  anterior  alveolar  margin  midway 
between  the  two  first  incisors — and  the  other,  the  basio-alveolar  line, 
viz.,  that  extending  frpm  the  anterior  margin  of  the  foramen  magnum, 
and  the  "alveolar  point."  Prominent  jaws  indicate  an  approach  to 
an  animal  type,  especially  when  associated  with  a  receding  forehead, 
and  the  greater  the  amount  of  prognathism  the  smaller  the  facial 
angle  (Figs.  96,  97,  and  98). 

Gnathic  Index. — The  degree  of  projection  of  the  upper  jaw  is 
expressed  by  the  Gnathic  Index,  which  represents  the  ratio  of  the  dis- 
tance between  the  "basion"  and  the  "alveolar  point,"  to  the  distance 
between  the  "basion"  and  the  "nasal  point,"  that  is,  the  point  of 
junction   of  nasal   and   frontal   bones  in  the   middle  line. 

Thus  the  Gnathic  Index  is  obtained  by  ascertaining  the  length  of 
the 

Basio-alveolar  line  X  lOO 
Basio-nasal  line. 

Amongst  the  Greeks  the  facial  angle  measured   100  degrees,  i.  e., 
the  basio-nasal  and  basio-alveolar  lines  were  equal  in  length. 
At  the  present  day  the  following  measurements  obtain: 


Race. 

Facial  angle. 

Gnathic  inde 

Europeans 

95  degrees 

96 

Chinese  . 

99 

Eskimos 

lOI 

Fiji  Islanders 

103 

Australian  natives 

85  degrees 

104 

The  dog  or  crocodile 

20  degrees 

Of  these — if  European  races  are  taken  as  a  type — are,  therefore, 
orthognathoiis,  the  Chinese;  Eskimos  and  Fijians  whose  gnathic  indices 
range  from  98  to  103,  would  be  mesognathous,  and  Australian  aborigines 
prognathous,  i.  e.,  103  or  moi'e. 

In  conclusion,  the  systematic  descriptions  of  the  dentitions  of  a 
European  man  would  read  thus: 

1.  Position  on  Maxillary  and  Mandibular  bones. 

2.  Dental  formula:  I  I  C  |  Pm  |  M  |  x  2  =  32. 


DESCRIPTIONS  OF  DEXTITIOXS  173 

3.  Heterodont.      Incisors  similar  in   shape.      I-   rather  smaller 

than  P.  Canines  more  sexual,  rather  larger  than  incisors, 
premolars  single  rooted  except  Pm^;  molars  decrease  in  size 
posteriorly,  the  third  molar  being  often  unerupted. 

4.  Enamel,  ortho-dentine,  cementum. 

5.  Gomphosis. 

6.  Diphyodont. 

7.  Horse-shoe  shaped,  movements  varied,  ginglymo-arthrodial 

joint.  Orthognathous  (95  to  98  Gnathic  Index).  Facial 
angle,  95  degrees;  microdont.  Dental  Index,  42. 

8.  Omnivorous. 

Referen'ces 

1.  Beddard.     "Mammalia."    The  Cambridge  Natural  History,  1902,  vol.  x. 

2.  Dubois.     " Pithecanthropus  erectus.    Eine  menschendhnliche  Uebergangsfortn  aiis  Java,"  1894. 

3.  Duckworth.     "A  Note  on  the  Dentition  of  Some  New  Guinea  Skulls,"  Trans.  Odonto  Soc, 
vol.  xxxix. 

4.  "  Encyclopasdia  Britannica,"  1910,  eleventh  edition. 

5.  Flower  and  Lydekker.     "An  Introduction  to  the  Study  of  Jilammals, "  1891. 

6.  Haeckel.    "The  Last  Link,  "  1898. 

7.  Lydekker.    iVIammalia,  Natural  History.     Concise  Knowledge  Library,  l&qj. 

8.  Selenka.    "Rassen  und  Zahnwechsel  des  Orang-utang,  "  Sitz-ber,  Akad.,  1896. 

9.  Smurthwaite.     "Practical  Anthropology,"  1912. 

10.  Zuckerkandl.     "  Die  Backenzahne  des  Menschen,"  Congress  der  Detitschen  und  Ostreirhischen 
anthropologischen  GeseUschaft,  1889. 


CHAPTER    X 


THE   ANATOMY   OF  THE   TEETH   OF   MAN 


Introductory. — General  Considerations. — Descriptions  of  the  Permanent  Incisors,  Canines, 
Premolars,  and  Molars,  their  Measurements,  Variations  of  Mensuration,  Coronal  Surfaces, 
Necks,  Roots,  Dates  of  Calcification,  Pulp  Chambers  and  Root  Canals,  Means  of  Identification, 
and  Surgical  Anatomy. — The  Deciduous  Teeth. — Age  Changes. 

Introductory. — It  is  necessary  at  the  outset  of  writing  a  descrip- 
tion of  the  human  teeth  to  postulate  that  by  virtue  of  the  operation 

Fig.  99 


The  left  maxilla  and  mandible  of  an  adult,  showing  ilu   ( 
X  {.     Cf.  Fig.  luu. 


spects  of  the  permanent  teeth. 


of  the  law  which  renders  an  individuality,  which  can  be  estimated 
on  careful  scrutiny,  peculiar  to  each  bone  or  muscle  or  viscus,  there 
are  no  two  dental  organs  which  possess  exactly  similar  morphological 


PLATE   I 


A  Human  Skull   in   Norma   Facialis.     X  y 


THE  ANATOMY  OF   THE   TEETH  OF  MAX 


175 


characteristics.  There  are  no  two  teeth  identical  in  every  particular; 
there  are  no  two  dental  arches  or  hard  palates  alike.  This  fact,  if 
thoroughly  elaborated,  might  be  turned  to  great  advantage  by  criminol- 
ogists and  others  who,  by  means  of  plaster  casts  of  the  teeth  and  jaws, 
would  probably  have  a  good  and  sure  adjunct  to  the  methods  of  the 
identification  of  offenders  against  the  law  by  means  of  finger  prints. 


Vertical  section  through  the  left  maxiUa  and  mandible  of  an  adult,  with  the  external  alveolar 
plates  removed  to  show  the  general  arrangements  of  the  roots  of  the  permanent  teeth,  the 
shapes,  sizes,  and  positions  of  their  pulp  cavities,  and  the  cancellous  character  of  the  bone  of 
their  sockets.     X  1. 


Hence,  an  account  of  the  gross  anatomy  of  the  teeth  of  man  must 
apply  only  very  generally  to  what  obtains  in  a  majority  of  the  speci- 
mens examined.  Types  only  can  be  detailed;  perfect  examples  are 
almost  impossible  to  find.  So  many  teeth  which  are  described  have 
undergone  slight  variations  of  pattern  or  age  changes  which  are  apt 


176  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

to  deceive  the  observer,  and  render  nugatory  any  anatomical  points 
on  which  he  is  hkely  to  la^"  a  certain  amount  of  emphasis.  The  same 
may  be  said  regarding  the  illustrations.  Xo  outline  drawing  of  a 
tooth  can  represent  its  real  architecture.  The  reader  is  begged,  there- 
fore, to  bear  in  mind  that  the  narration  which  now  ensues  is,  at  best, 
merely  an  attempt  to  portray  verbally  and  visually  its  most  important 
particulars. 

General. — A  tooth  consists  of  a  crown,  a  neck,  and  a  root  or  roots. 
Of  these  the  former  usually  presents  above  the  gum,  the  latter  is 
implanted  in  an  alveolar  socket,  and  the  neck  is  the  region  Avhich 
intervenes  in  the  neighbourhood  of  the  gingival  trough.  If  a  tooth 
remains,  however,  imbedded  in  the  substance  of  the  bone  of  the  jaw, 
it  still  generally  possesses  these  three  main  parts  (Figs.  5  and  6), 
although,  if  its  non-erupted  condition  should  have  induced  a  cyst 
of  the  jaw — whether  it  be  a  dental  cyst,  a  follicular  odontome  or  an 
odontocele — one  or  more  of  these  parts  may  be  absent.  Teeth  erupt- 
ing in  anomalous  situations,  such  as  the  floor  of  the  nasal  fossae,  the 
exterior  of  the  cheek,  the  interior  of  the  antrum,  the  surface  of  the 
ill-formed  bone  found  in  certain  teratomata,  etc.,  may  also  possess 
these  parts  in   a  modified   degree.      (See  Figs.  3  and  4.) 

For  graphical  purposes  the  writer  proposes  to  relate  the  anatomical 
characteristics,  first,  of  the  maxillary  permanent  series  of  the  right 
side,  then  the  mandibular  teeth,  and  then  the  chief  distinguishing 
features  of  the  members  of  the  deciduous  dentition  also  of  the  same 
side. 

THE    MAXILLARY    SERIES 

The  Incisors. — The  incisors  (lucidere — to  cut  into)  are  eight  in 
number,  four  maxillary  and  four  mandibular.  The^'  are  called  the 
First  and  Second,  or  clinically  and  vulgarly  the  "central"  and  "lateral." 
They  are  the  teeth  which  are  implanted  in  the  premaxillarj'  bone  in 
the  upper,  and  the  corresponding  members  in  the  lower  jaw.  Their 
crowns  roughly  resemble  the  ivory  mouth-piece  of  a  flute.  The}'  possess 
one  root  and  one  pulp  canal.  Occasionally,  there  may  be  traces  of  a 
second  root. 


THE  MAXILLARY  SERIES  177 

The  First  Right  Maxillary  Permanent  Incisor. — This  tooth  is  situated 
on  the  right  of  the  midline  of  the  face,  that  is,  to  the  right  of  that  part 
of  the  palatal  process  of  the  right  superior  maxillary"  bone  which 
articulates  with  the  left  superior  maxillary  bone.  In  France  it  is 
popularly  termed  "la  palette"  (the  battledore),  by  reason  of  it?  shape 
and  of  its  size  being  greater  than  that  of  the  second  incisor. 

(a)  Mean  Measurements. — The  extreme  length  from  incisive 
edge  to  apex  of  root  is  2^  mm. :  extreme  width  across  the  broadest 
part  of  the  crown  is  9  mm.  It  is  usualh"  a  very  large  tooth.  Black 
gives  in  his  "Dental  Anatomy"  the  following  figures:  Average  length 
of  crown,  0.39  inch;  of  root,  0.49  inch;  of  length  over  all.  0.88  inch. 

Variations  of  mensuration  range,  in  rare  specimens,  from  14  mm. 
to  32  mm.  in  extreme  length,  and  5.75  mm.  to  10  mm.  in  extreme 
width. 

(6)  Coronal  Surfaces. — The  coronal  Surfaces  are  four  in  number. 
and  there  are  two  angles. 

(z)  Labial  Surface* — It  measures  in  extent  9  mm.  by  12.5  mm. 
Triangular  in  shape,  its  base  is  at  the  incisive  edge.  It  is  convex  from 
above  downward  and  from  side  to  side.  It  terminates  at  the  gingival 
margin  by  a  rounded  border  slightly  raised  from  the  neck,  and  curving 
downward  on  the  mesial  and  distal  surfaces,  approaches  the  incisive 
edge  ver>'  considerably.  Thus  the  upper  border  of  a  labial  surface 
which  is  12.5  mm.  in  a  vertical  direction  from  the  incisive  edge  is 
only  8  mm.  on  the  mesial  surface. 

It  is  smooth  and  shiny  in  appearance,  and  in  the  majorit\-  of  cases 
its  surface  is  somewhat  broken  up  by  numbers  of  small  longitudinal 
or  horizontal  grooves  (imbrication  lines),  which  represent  an  imper- 
fected  condition  of  the  enamel.  This  remark  applies  to  the  enamel 
of  the  other  teeth  generally. 

(//)  Lingual  Surface. — This  is  more  triangular  in  outline  than  the 
former,  though  its  edges  are  more  rounded.  It  is  concave  from  above 
downwards  and  also  from  side  to  side,  but  the  vertical  concavity  does 

*  In  France  anatomists  allot  different  names  to  the  coronal  surfaces.  Thus  the  "anterior"  and 
"posterior"-  aspects  correspond  to  the  labial  and  lingual  surfaces  of  incisors  and  canines,  and  to 
mesial  and  distal  surfaces  of  the  premolars,  while  the  buccal  is  the  "external"  and  the  palatine  is 
the  "internal"  or,  according  to  Barden'  and  Dieulafe  and  Herpin,^  the  "vestibular"  face. 


178  THE  ANATOMY  OF  THE  TEETH  OF  MAN 

not  extend  to  the  cutting  edge  or  lower  border  which  runs  in  a  straight 
Hne.  In  many  incisors  there  is  evidence  of  a  sHght  elevation  of  an 
aborted  cingulum  on  the  upper  border  of  these  two  surfaces,  which 
shows  itself  as  an  inconspicuous  prominence  in  the  central  axis  of 
the  tooth. 

(in)  The  Mesial  surface  is  smaller  than  the  distal.  It  is  slightly 
convex  in  both  directions.  Triangular  in  outline,  the  apex  is  placed 
below,  the  base  being  largely  encroached  upon  by  a  second  triangle 
formed  by  the  cementum  at  the  neck  of  the  tooth. 

Fig.  ioi        Fig.  102        Fig.  103       Fig.  104       Fig.  105     Fig.  106 

■■  £&  i^a  .^  ^  /  <    1  ^m  11  .vO 

I 


Fig.  ioi. — The  maxillary  first  incisor — Labial  aspect.      X  -}-. 

Fig.  102. — The  same — Lingual  aspect.  ^j,,. 

Fig.  103. — The  same — Mesial  aspect.  ^|      !^ 

Fig.  104. — The  same — Mesio-distal  section. 

Fig.  105. — The  same — Labio-lingual  section. 

Fig.  106. — The  same — Various    horizontal    sections:      A,    through    the    crown;   B,      O       ^ 
through   the  crown;  C,  the  neck;  D,  mid-portion;  E,  near  the  apex. 

(iv)  The  Distal  surface  is  also  triangular  with  the  same  encroach- 
ment of  the  cervical  triangle;  the  distance,  however,  between  the 
apices  of  these  two  triangles  is  greater  on  the  latter  than  on  the  former 
surface,   the  measurements  being  mesially  7  mm.;  distally,   8.5  mm. 

(v)  The  Angles. — The  mesial  angle  is  a  right  angle,  at  times  rather 
more  than  a  right  angle;  the  distal  is  an  obtuse  angle. 

Newly  erupted  incisors  generally  possess  three  tubercles  on  the 
cutting  edge  which,  for  some  unexplained  reason,  disappear  in  a  normal 
physiological  manner  as  the  years  pass  by. 

(c)  Neck. — The  Neck  of  the  tooth  is  formed  by  the  convergence 
of  the  four  surfaces,  and  is  represented  by  their  upper  borders.  It 
does  not  lie  in  the  same  horizontal  plane  throughout,  but,  as  already 


THE  MAXILLARY  SERIES  179 

mentioned,  clips  down  mesially  and  distally  at  spots  situated  midway 
between  the  labial  and  lingual  surfaces. 

{d)  Root. — The  Root  is  cone-shaped,  and  nearly  cylindrical.  Its 
greatest  circumference  is  not  at  the  neck,  but  about  one-third  of  the 
distance  between  the  neck  and  the  apex.  Its  sides  are  not  equally 
convex  nor  straight.  The  mesial  aspect  -is  the  most  convex,  and  at 
the  same  time  it  is  the  most  vertical,  the  distal  aspect  being  the  most 
flattened  and  curved.  It  generally  tapers  gradually  to  its  extremity, 
which  is  frequently  curved  or  deflected,  and,  in  a  great  many  cases, 
roughened  and  enlarged  by  a  deposit  of  lacunated  cementum.  The 
apical  foramen  which  transmits  the  afferent  and  efferent  bloodvessels 
and  terminations  of  the  nervous  system  of  the  pulp  is  generally  clearly 
marked.  But  it  is  often  most  difficult  to  see  and  its  orifice  so  occluded 
as  to  admit  of  no  passage  of  the  finest  bristle  which  could  possibly  be 
manufactured. 

{e)  Calcification. — The  Calcification  of  this  tooth  begins,  accord- 
ing to  Norman  Broomell,^  in  three  centres  of  ossification,  in  the  first 
year  post  iiatuin,  and  is  completed  as  far  as  its  outer  appearance  is 
concerned  by  the  tenth  to  the  eleventh  year,  and  eruption  begins 
about  the  seventh  year  and  ninth  month  (30.5  per  cent.),  according  to 
James  and  Pitts. ^- 

(/)  Pulp  Canal. — The  Pulp  Canal,  as  seen  in  the  labio-lingual 
direction,  conforms  closely  to  the  general  shape  of  the  tooth.  At  the 
tenth  year  it  resembles  two  narrow  cones,  the  bases  of  which  are 
placed  on  a  level  with  the  cervical  region  of  the  tooth,  the  upper  or 
radicular  cone  being  the  larger  and  the  narrower.  Mesio-distally, 
the  lower  edge  of  the  pulp  cavity  is  the  broadest  part,  follows  the 
same  direction  as  that  of  the  cutting  edge,  has  up  to  the  fifteenth  year 
three  cornua — of  which  the  central  is  the  least  marked,  and  disappears 
about  that  age — the  others,  named  mesial  and  distal  respectivelj^, 
remaining  up  to  old  age. 

Transversely  the  pulp  canal  is  almost  cylindrical  in  outline. 

ig)  Identification. — Identification  of  this  incisor  may  be  effected 
by  the  following  means:  If  the  tooth  is  held  in  a  horizontal  position 
between  the  left  forefinger  and  thumb,  with  the  con\ex  surface  of 
the  crown  lying  upwards  and  the  root  awa>'  from  the  spectator,  the 


180  THE  ANATOMY  OF   THE  TEETH  OF  MAN 

sharper  angle  of  the  cutting  edge  will   point  to  the  side  to  which   it 
belongs. 

(/z)  Surgical  Anatomy. — Subgingival  tartar  may  collect  on  the 
mesial  and  distal  aspects  of  the  cervical  region  of  the  root.  Caries 
begins  most  frequently  interstitially;  that  is,  on  the  mesial  aspect. 
Black, ^  who  has  most  thoroughly  investigated  and  charted  the  posi- 
tions of  dental  caries,  gives  the  following  percentages:  Labial  surface, 
3.2;  Lingual,  2.6;  Mesial,  31.6;  Distal,  26.3,  and  Mesial  edge,  1.5. 
Magitot's  computation  is  that  6  per  cent,  of  the  superior  incisors  are 
carious. 

In  England  it  is  generally  believed  that  the  first  permanent  molar 
is  most  frequently  a  victim  to  caries."  In  this  connexion  the  reader 
must  compare  Black's  figures  regarding  this  tooth.  When  treating 
diseases  of  the  pulp,  the  chamber  should  be  opened  by  drilling 
through  the  enamel  and  dentine  in  the  centre  of  the  lingual  surface, 
in  the  direction  of  the  long  axis  of  the  tooth.  An  alveolar  abscess 
connected  with  this  tooth,  points  over  the  external  alveolar  plate 
above  the  apical  region.  Rotation  of  the  root  is  indicated  in  the 
operation  of  extraction.  In  orthodontics  the  thinness  of  the  external 
alveolar  plate  allows  with  facility  the  forward  advancement  of  the 
teeth.  Fusion  of  this  with  the  following  tooth  sometimes  occurs  (true 
gemination),  and  extremely  rarely  with  its  fellow  of  the  opposite 
side  (false  gemination).  It  is  frequently  hypoplasic;  or  congenital 
syphilis  leaves  its  mark  in  the  form  of  a  notch  on  the  incisive  edge,  and 
a  general  dwarfing  of  the  crown. 

The  Second  Right  Maxillary  Permanent  Incisor. — In  external 
configuration  it  is  approximate  to  that  of  the  first  incisor.  It  is  a 
smaller  tooth  in  every  respect  and  its  architecture  is  not  so  well 
pronounced.     It  is  frequently  suppressed  (Figs.  43  and  44). 

(a)  Mean  Measurements. — Extreme  length,  23  mm.  Extreme 
width,  6.5  mm.  According  to  Black:  Average  length  of  crown,  0.34 
inch;  of  root,  0.51;  length  over  all,  0.85  inch. 

Variations  of  mensuration,  31.5  mm.  to  18  mm.;  7  mm.  and  55  mm. 

(&)  The  Crown. — The  extent  of  the  {i)  Labial  Surface  is  10  mm. 
X  6.5.  mm.  It  is  more  convex  in  both  directions  than  its  neighbour, 
and  the  upper  border  is  less  rounded.     Its  surface  is  smooth,  often  less 


THE  MAXILLARY  SERIES 


181 


scoured  by  lines  of  minute  pits  or  fissures  than  the  first  incisor,  and 
approximates  more  closely  to  the  shape  of  an  isosceles  triangle  than 
the  other.  The  incisive  edge  often  presents  two  small  tubercles  which 
may  remain  till  the  eleventh  year. 

(ii)  The  Lingual  Surface  is  more  extensive  vertically  than  the 
former.  Then  it  may  measure  1.5  mm.  more  in  depth  from  above 
downwards.  Its  concavities  are  very  marked  and  the  cingulum  is 
often  raised  at  the  gingival  margin  into  a  large  prominence. 


Fig.  107  Fig.  io8  Fig.  109  Fig.  iio  Fig.  hi 


i 


u 


y 


Fig.   107. — The  maxillary  second  iiicisor — Labial  aspect.      X  y. 
Fig.  108. — The  same — Lingual  aspect. 
Fig.  109. — The  same — Distal  aspect. 
Fig.   ho. — The  same — Mesio-distal  section. 
Fig.   III. — The  same — Labio-lingual  section. 

Fig.   112. — The   same — Various  horizontal   sections:     A,  through   the  crown; 
neck;   C,  the  root;  D,  near  the  apex. 


Q    o 


{Hi)  The  Mesial  and  [iv)  Distal  Surfaces  closely  approach  one 
another  in  size  and  shape.  While  the  former  is  flat  and  only  slightly 
convex,  the  latter  is  particularly  well  rounded.  The  mesial  angle  is 
obtuse,  the  distal  angle  rounded  and  still  more  obtuse. 

The  longitudinal  axis  of  the  tooth  is  in  a  straight  line,  the  position 
of  the  radicular  apex  occupying  a  plane  which  passes  through  the 
centre  of  the  tooth  and  joins  the  incisive  edge  midwaj'  between  the 
two  angles. 

{c)  Neck. — The  v-shaped  outline  of  the  Neck  is  not  so  marked  as 
in  the  first  incisor.  The  cingulum  varies  very  greatly  and  at  times 
may  be  duplicated. 

{d)  Root. — The  Root  is  cone-shaped,  but  considerably  flattened 
from  side  to  side.  It  may  be  bifurcated.  Its  mesial  and  distal  aspects 
are  much  broader  than  the  labial  and  lingual,  the  proportion  of  the 


182 


THE  ANATOMY  OF   THE   TEETH  OF  MAN 


Fig.  113 


two  being  as  4  is  to  6.  The  apex  is  frequently  deflected  to  one  or  other 
side,  most  often  towards  the  distal.  As  in  the  first  incisor,  the  apical 
foramen  is  most  frequently  so  small  as  to  be  indiscernible. 

(e)  Calcification. — The  Calcification  begins  during  the  first  year 
post  natum,  and  is  superficially  completed  by  the  tenth  to  the  eleventh 
year,  eruption  taking  place  between  the  ninth  year  and  third  month 
in  35.4  per  cent,  of  cases." 

(/)  Pulp  Canal. — The  Pulp  Canal  of  this  tooth  is,  relatively  to  the 
size  of  the  tooth  itself,  greater  than  that  of  the  first  incisor.  It  follows, 
therefore,  that  it  is  very  little  smaller  than  that 
which  obtains  in  the  neighbouring  tooth,  and  that 
its  dentinal  and  enamel  coverings  are  naturally 
thinner.  The  cornu  are  similar  to  those  already 
described,  a  central  one  may  be  present,  but  the 
mesial  cornu  maj'  be  a  little  more  elongated  than 
the  opposite  one. 

{g)  Identification. — Identification  of  this  in- 
cisor may  be  effected  by  similar  means  to  that 
employed  for  the  first  incisor.  The  sharper  angle 
of  the  cutting  edge  points  to  the  side  to  Avhich  it 
belongs. 
fjl'^    •*  "^  ''  (^-^  Surgical    Anatomy. — Caries    affects    the 

fi)   i   '  various  surfaces  as  follows:     Labial,  1.6;  Lingual, 

0.6;  Mesial,    28;    Distal,   15.5;    Incisive  edge,    1.3 
per  cent.,  and  on  any  surface  7.4  per  cent.    The 
pulp  chamber    must  be  opened  similarly  to  that 
already  previously  described.     An  abscess  found 
in  connexion  with    this    tooth    extends  into,  and 
opens  over,  the  side  of   the   palate,  by  reason  of 
the  fact  that,  when  in  situ,  the  apex  of  the  root  has  a  tendency  to  look 
inwards  towards  the  central  line  of  the  hard  palate.     Dental  cysts  arise 
frequently  from  this  tooth  in  the  proportion  of  i  to  10. 

The  Canines. — The  canines  are  four  in  number,  situated  at  the 
angle  of  the  alveolar  processes  of  the  jaws,  and  on  account  of  their 
position  are  valuable  agents  in  maintaining  the  character  of  the  face, 
and  imparting  to  their  possessor,  according  as  they  are  large  and  promi- 


Labio-lingual  section 
through  a  maxillary  in- 
cisor, in  situ,  to  show 
the  osseous  relationships. 
X  +. 


THE  MAXILLARY  SERIES  183 

nent  or  not,  a  bestial  or  beautiful  aspect  of  countenance.  From  this 
aesthetic  point  of  view,  therefore,  they  constitute  the  most  important 
of  all  the  teeth  of  Man.  They  are  called  canines  from  their  large  size 
and  cardinal  function  in  the  CanidcE,  their  prominence  being  clearly 
and  obviously  noticed  in  the  members  of  the  carnivorous  type  of 
animal.  The  maxillary  canines  are  designated  "Eye  teeth"  by  the 
ignorant  and  uninformed,  this  antiquated*  and  incorrect  term 
appearing  to  arise  from  the  widespread  belief  that  ocular  disturbances 
very  often  took  their  origin  from  these  teeth. 

Those  situated  in  the  maxillae  are  the  teeth  which,  placed  in  those 
bones,  erupt  beyond  the  intermaxillary  suture,  provided  they  are 
not  too  far  behind.  They  are  readily  distinguished  by  their  great 
length,  and  dimensions,  which  surpass  every  other  member  of  the 
dental  series. 

The  Right  Maxillary  Permanent  Canine. — (a)  Mean  Measure- 
ments.— Greatest  length,  extending  from  apex  of  root  to  the  extremity 
of  the  cusp,  is  27  mm.,  width  in  coronal  region  8  mm.  It  is  usually 
a  verj'  large  tooth,  and  is  infrequently  missing  from  the  dental  arch. 

Black's  measurements  are:  Average  length  of  crown,  0.37  inch;  of 
root,  0.68  inch;  total  length,  1.05  inches. 

Variations  of  Mensnratiou:  8  to  38  mm.  in  length  and  5.5  to  9  mm. 
in  width. 

{b)  Crown. — The  Crown  is  somewhat  cone-shaped,  with  a  morpho- 
logical modification,  chiefly  on  the  distal  side.  It  has  four  surfaces, 
labial,    lingual,   mesial,   and  distal. 

(?)  The  Labial  Surface  is  very  convex,  the  most  prominent  part 
being  at  the  junction  of  the  lower  two-thirds  with  the  upper  third. 
The  upper  border  is  almost  on  a  level  with  the  root  surface,  the  lower 
border,  sharp  and  pointed,  is  shorter  on  the  mesial  than  on  the  distal 
side.  This  surface  is  divided  into  two  unequal  parts  by  a  ridge  of 
enamel,  the  direction  of  which  more  or  less  coincides  with  the  longi- 
tudinal axis  of  the  tooth,  of  which  the  mesial  side  slopes  off  gradually 
in  a  convex  fashion,  to  the  mesial  surface  of  the  tooth,  while  the  other 
may  even  be  slightly  concave,  or  at  all  events,  flattened.    In  some  speci- 

*  To  Galen  (131  a.d.)  is  credited  the  belief  that  these  teeth  receive  branches  from  the  nerves 
which  supply  the  eyes. 


184  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

mens  it  is  distinctly  grooved  from  above  downwards,  one  on  either 
side  of  the  median  ridge.  The  ridge  terminates  at  the  cusp  of  the 
tooth.  The  lower  border  of  the  surface  is  pointed  at  the  cusp  and 
runs  mesially,  to  end  in  a  slightly  obtuse  angle,  and,  distally,  in  an 
extremely  obtuse  angle. 

Pig.  114  Fig.  115  Fig.  116  Fig.  117  Fig.  118  Fig.  119 


Fig.  114. — The  maxillary  canine — Labial  aspect.     X  l-. 

Fig.  115. — The  same — Lingual  aspect. 

Fig.  1 16. — The  same — Mesial  aspect. 

Fig.  117. — The  same — Labio-lingual  section. 

Fig.  118. — The  same — Mesio-distal  section. 

Fig.  119. — The  same — Various  horizontal  sections:  .4 ,  through  the  crown ;  5,  throug 
the  crown;  C,  the  neck;  D,  the  root;  £,  near  the  apex. 


{ii)  Lingual  Surface. — This  is  more  triangular  than  the  preceding. 
It  is  concave  from  side  to  side  and  from  above  downwards.  Like  the 
preceding,  it  is  roughly  divided  into  two  parts,  by  a  vertical  ridge  of 
enamel,  having  on  either  side  a  rounded  hollow,  the  depth  and  extent 
of  which  varies  very  greatly  in  every  subject.  The  upper  and  lower 
ends  of  this  enamel  edge  terminate  in  prominent  elevations,  of  which 
the  former  is  the  middle  portion  of  the  cingulum,  the  other  the  thicken- 
ing of  the  cusp  of  the  tooth  itself.  There  is  a  slight  elevation  of  the 
mesial  and  distal  borders  into  crests. 

{Hi)  The  Mesial  Surface  is  flattened  from  before  backwards,  and 
from  side  to  side.  It  is  less  triangular  in  outline  than  that  of  the  first 
incisor,  and  the  crown  of  the  tooth  passes  almost  imperceptibly  into 
the  neck  and  root,  the  junction  being  very  nearly  in  a  straight 
horizontal  line. 

(izO  The  Distal  Surface  is  similar  to  the  preceding,  but  at  its  lower 
portion,  at   the  junction   of   the   distal   part  of   the   lower   border,    a 


THE  MAXILLARY  SERIES 


185 


Fig.  120 


considerable  amount  of  thickening  of  tlie  crown  occurs,  and  gives  the 
characteristic  appearance  to  the  maxillary  canine. 

{v)  The  Angles  are  obtuse,  the  distal  being  markedly  so,  and  very 
blunt  and   rounded. 

(c)  Neck. — The  Neck  is  ill  defined,  the  enamel  gradually  becoming 
thicker  as  it  approaches  the  cusp  of  the  tooth.  In  some  specimens 
the  neck  is  only  distinguished  by  the  differences  in  appearance  of  the 
enamel  and  cementum. 

{d)  Root. — The  Root  is  a  laterally  flattened  cone.  Its  remarkable 
length  has  already  been  alluded  to.  Across  its  mesial  or  distal  aspect 
it  may  measure  8  mm.,  across  the  labial  5  mm., 
and  across  the  lingual  4  mm.  Sometimes  these 
broader  surfaces  exhibit  traces  of  a  groove 
and  become  in  that  respect,  somewhat  pre- 
molariform  in  character.  Its  apical  region 
is  often  deflected. 

(<?)  Calcification.  —  Calcification  begins 
during  the  third  year  after  birth,  and  is 
superficially  completed  from  the  twelfth  to 
the  thirteenth.  Its  eruption  precedes  its 
completion  of  calcification  and  occurs  about 
the  tenth  year  and  sixth  month. 

(/)  Pulp  Canal. — The  shape  of  the'  Pulp 
Canal  follows  closely  the  exterior  aspect  of 
the  tooth.  Transversely,  the  outer  half  is 
broader  than  the  lingual  portion. 

(g)  Identification. — This  can  be  accom- 
plished by  the  same  means  as  for  the  incisors. 
By  taking  into  consideration  the  location  of 
the  prominence  on  the  distal  surface  of  the 

crown,  it  is  always  easy  to  ascertain  to  which  side  of  the  mouth  the 
tooth  belongs. 

ih)  Surgical  x\natomy. — The  apical  foramen  is  closed,  generalh- 
speaking,  at  the  time  of,  or  immediately  after  the  eruption  of,  the 
tooth.  This  tooth  is,  of  all,  the  least  frequenth'  missing,  and  the 
most  frequenth'  misplaced  in  the  dental  arch,  cither  erupting  high  up 


ie 


7 


Labio-lingual  section  through 
a  maxillary  canine,  in  sittc,  to 
show  its  osseous  relationships. 
X  h 


186  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

in  the  external  alveolar  area,  or  inside  the  line  of  the  neighbouring 
teeth.  It  often  remains  embedded  in  the  jaw  in  an  encysted  or  normal 
condition,  and  adopts  an  oblique  or  a  horizontal  position  in  the  bone 
(Fig.  5  and  6).  Once  fully  grown  and  completely  in  place,  the  position 
of  the  maxillary  canines  varies  less  frequently,  and  to  a  less  extent, 
than  any  other  tooth,  as  a  result  of  changes  in  the  jaw. 

The  Percentage  of  Caries. — The  interstitial  surfaces  are  more  fre- 
quently attacked  than  the  self-cleansing  surfaces.  Caries  of  the  cusp 
is  not  very  rare.  Black's  figures  are:  Mesial  caries,  i6;  Distal,  ii; 
Labial,  i.6;  Lingual,  0.6,  and  cutting  edge,  i.8.  Magitot's  figures 
are,  for  any  surface  of  the  whole  tooth,  4.4  per  cent. 

The  Maxillary  Premolars. — Each  maxilla  possesses  two  premolars, 
and  on  either  side  of  the  mandible  there  is  also  the  same  number. 
They  are  the  fourth  and  fifth  teeth  from  the  midline,  and  occur  between 
the  canine  and  the  molars.  They  replace  the  molars  of  the  deciduous 
dentition.  They  are  the  homologues  of  the  third  and  fourth  premolars 
of  the  typical  mammalian  dentition. 

The  synonym  "bicuspid,"  although  it  has  passed  for  many  years 
into  common  daily  parlance,  is  not  absolutely  correct,  because  many 
other  teeth  possess  two  cusps.  It  is  advisable  to  be  strictly  accurate, 
and  to  speak  of  this  tooth  as  a  premolar,  which  signifies  that  it  is 
placed  in  the  dental  arch  in  front  of  the  molars,  and  that  it  has  had 
a  molariform  predecessor. 

Some  authors  aver  that  the  premolar  represents  a  fusion  of  two 
primitive  haplodont  cones,  as  has  been  explained  in  Chapter  VIII. 
This  is  probably  erroneous,  as  it  would  imply  a  lateral  fusion  of  two 
distinct  and  different  dentitions,  of  which  the  rate  of  growth  would 
be  nearly  equal.  The  inner  cusp  may  be  considered  as  an  elevation 
of  the  inner  portion  of  the  cingulum. 

The  First  Right  Maxillary  Premolars. — (a)  Mean  Measurements. 
— Extreme  length,  20  mm.;  extreme  width,  6.5  mm.  Length  of  crown, 
0.32  inch;  or  root,  0.48  inch;  total  length,  0.80  inch. 

Variations  of  Mensuration. — The  largest  may  equal  28.5  mm.  in 
extreme  length,  and  8  in  extreme  breadth,  and  the  smallest  13  mm. 
in  extreme  length  by  6.5  in  extreme  width. 


THE  MAXILLARY  SERIES 


187 


[b)  Crown. — The  Crown  presents  five  surfaces  for  examination: 
{i)  Labial;  {ii)  lingual;  {Hi)  mesial;  {iv)  distal,  and  ii)  morsal  or 
occluding. 

It  is  roughly  cuboidal  in  shape,  the  internal  or  lingual  portion  being 
slighth'  the  smaller  of  the  two. 


Fig.  121 


u 


Fig.  123 


1 


Fig.  124 


Fig.  125 


Fig.   121. — The  maxillary  first  premolar.     Distal  aspect.       X  \. 
The  same — Mesial  aspect. 
The  same — Buccal  aspect. 
The  same — Bucco-lingual  section. 
— The  same — Mesio-distal  section. 

— The  same — Various  horizontal  sections:    A,  through  the  crown;  B,  through 
the  crown;  C,  through  the  crown;  D,  the  neck;  E,  the  roots;  F,  the  apices. 


Fig. 

122.- 

Fig. 

123.- 

Fig. 

124. 

Fig. 

125- 

Fig. 

126. 

{i)  The  Labial  surface  is  convex  from  above  downwards,  and  from 
side  to  side.  Very  striking  in  its  resemblance  to  the  corresponding 
surface  of  the  crown  of  the  canine,  it  often  presents  the  median  ridge 
and  lateral  vertical  grooves  described  in  dealing  with  that  tooth. 
The  difference  lies  mainly  in  the  fact,  that  here  the  grooves  are  not 
entirely  vertical,  but  converge  somewhat  at  the  lower  border.  The 
outline  of  this  surface  is  less  triangular  than  that  of  the  other  anterior 
teeth,  becoming  more  diamond-shaped.  The  point  of  the  cusp  is  sharp, 
but  rounded  on  the  morsal  surface. 

{ii)  Lingually  viewed,  the  surface  is  very  convex  in  both  directions, 
and  possesses  no  vertical  ridge  or  groo\es.  The  superficies  is  con- 
siderably less  than  that  of  the  former. 

{Hi)  Mesial. — This  surface  is  roughly  quadrilateral  in  outline,  the 
lower  portion  being  slightly   protuberant.      It  is  slightly  concave  in 


188  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

both  directions,  and  the  vertical  concavity  may  amount  sometimes  to 
a  grooving. 

{iv)  Distal. — Similar  to  the  preceding  except  for  its  convexities. 
It  is  probably  relatively  larger  in  area,  and  the  prominence  of  the 
lower  portion  more  pronounced. 

{v)  The  M or  sal  Surface  is  of  the  shape  of  an  irregular  trapezoid. 
The  greatest  diameter  is  in  the  labio-lingual  direction  on  account  of 
its  lateral  flattening.  As  a  result  of  a  slight  convergence  of  the  mesial 
and  distal  surfaces,  the  labial  surface  is  the  largest  of  the  three.  Its 
angles  are  very  rounded  and  turned  towards  the  centre  of  the  tooth. 
Of  the  cusps,  the  outermost  is  the  larger,  and  is  separated  from  the 
other  by  a  deep  sulcus.  It  is  surmounted  by  four  ridges  or  crests  of 
enamel,  which  uniting  to  form  the  prominence  of  the  outer  cusp, 
pass,  one  forwards  to  the  outer  mesial  angle,  the  second  backwards  to 
the  outer  distal  angle,  the  third  inwards  to  the  middle  of  the  sulcus, 
and  the  fourth,  indistinctly  to  unite  outwards,  with  the  median  ridge 
of  the  enamel  on  the  labial  surface.  The  lingual  cusp  is  less  prominent, 
its  point  less  pronounced,  and  more  rounded.  Like  the  other,  ridges 
of  enamel  pass  outwards,  forwards,  and  backwards.  The  floor  of  the 
morsal  surface  is  traversed  by  certain  additional  grooves,  often 
amounting  to  fissures,  which,  crossing  in  a  mesio-distal  direction,  may 
bifurcate  near  either  extremity,  and  pass  outwards  and  forwards,  or 
simply  turn  outward. 

(c)  Neck. — The  Neck  is  nearly  horizontal,  and  dips  down  very 
slightly  on  the  mesial  and  distal  surfaces. 

id)  Root. — The  Root  is  very  flattened  from  side  to  side,  and  pre- 
sents on  its  mesial  and  distal  aspects  a  deep  grooving,  which  is  often 
sufficiently  pronounced  as  to  divide  into  two  roots,  each  having  a 
pulp  canal.  The  groove  on  the  mesial  aspect  is  greater  than  the 
other.  It  is  probable  that  the  first  premolar  is  undoubtedly  bi-rooted 
in  almost  60  per  cent,  of  cases.  The  roots  may  be  joined  through  only 
half  their  length,  though  the  usual  condition  is  to  find  them  united 
through  two-thirds,  or  even  five-sixths,  of  their  length.  Rarely,  three 
roots  may  be  present,  in  which  case  two  are  labially,  and  the  other 
lingually  placed,  an  anomaly  which  probably  is  atavistic,  as  three- 
rooted  first  premolars  are  constant  in  the  Anthropoidia,  as  described 


THE  MAXILLARY  SERIES 


189 


Fig.  127 


in  Chapter  IX.      There  is  a  great  tendency  for  the   roots  to  diverge 
at  their  apical  regions. 

(c)  Calcification. — Calcification  begins  about  the  fourth  year  and 
is  superficially  completed  about  the  eleventh  to  the  twelfth.  The  tooth  is 
erupted  between  the  ages  of  nine  years,  and  nine  years  and  six  months. 

(/)  Pulp  Chamber. — The  Pulp  Chamber  closely  imitates  the  out- 
lines of  the  crown.  There  are  two  cornua,  each  of  which  projects 
into  the  buccal  and  the  lingual  cusp,  the 
former  being  the  larger  of  the  two.  On  ac- 
count of  the  excessive  lateral  flattening  of 
the  tooth,  the  greatest  diameter  of  the  pulp 
canal  occurs  in  a  labio-lingual  direction. 
There  are  two  pulp  canals,  the  bifurcation 
of  the  pulp  chamber  occurring  in  the  imme- 
diate neighbourhood  of  the  neck  of  the  tooth. 

(g)  Identification. — The  Identification  of 
this  tooth  may  be  accomplished  by  holding 
the  tooth  with  its  crown  towards  the  observer, 
and  its  larger  external  cusp  pointing  in  the 
same  direction.  The  deeper  grooving  of  the 
root — on  the  mesial  or  canine  aspect — points 
towards  the  side  to  which  the  tooth  belongs. 

Qi)  Surgical  Anatomy. — In  opening  up 
the  pulp  chamber  or  canals,  the  point  to 
select,  is  in  the  centre  of  the  chief  groove  on 
the  morsal  surface.  Care  must  be  taken  in 
this  operation,  or  the  I'oots  may  be  split.  Caries  affects  this  .tooth 
most  frequently  on  the  distal  surface,  least  frequently  on  the  lingual, 
as  the  following  figures  (Black)  show:  Mesial,  12.6;  Labial,  1.3; 
Distal,  20;  Lingual,  o.l;  Morsal,  6.6.  Out  of  Magitot's  10,000  cases, 
the  first  maxillary  premolar  was  carious  949  times,  giving  a  percentage 
of  9.4.  For  the  prevention  of  overcrowding  and  irregularity  in  the 
position  of  the  teeth,  the  extraction  of  this  tooth  before  eruption  is 
undertaken  with  successful  results.  It  is  necessary,  however,  before 
removal  of  the  deciduous  molar,  to  ascertain  by  means  of  the  .v-rays, 
whether  the  tooth  is  present  or  not. 


Labio-lingual  section  through 
a  maxillary  first  premolar,  in 
situ,  to  show  its  osseous  relation- 
ships.     X  \. 


190 


THE  ANATOMY  OF  THE  TEETH  OF  MAN 


The  Second  Right  Maxillary  Premolar. — This  tooth  is  the  fifth 
in  the  series  from  the  maxillary  suture.  It  closely  resembles  the  morpho- 
logical features  of  the  first  premolar,  but  difTers  mainly  in  two  par- 
ticulars. It  is  very  slightly  smaller,  its  alveolar  parts  are  confluent, 
and  give  it  the  appearance  of  possessing  only  one  root.  There  may 
be  two  pulp  canals  present.  Its  cusps  are  often  shorter  and  the  ridges 
more  rounded  than  in  the  first  premolar. 

(c)  Mean  Measurements. — Extreme  length,  22  mm.;  extreme 
width,  5  mm. 

Variations  of  Mensuration. — The  largest  examined  was  28  mm. 
in  extreme  length  and  8  mm.  across  the  broadest  part  of  the  crown 
in  a  mesio-distal  direction,  the  smallest  16  mm.  and  the  same  width. 


Fig.  128 


Fig.  130 


Fig.  131 


Fig.  132 


Fig. 129 


/  \ 


w 


-The  maxillary  second  premolar.     Mesial  aspect.      X  r. 
-The  same — Distal  aspect. 
-The  same — Buccal  aspect. 
-The  same — Bucco-lingual  section. 
-The  same — Mesio-distal  section. 

-Various  horizontal  sections:      A,  through   the  crown;    B,  through  the 
crown;  C,  the  neck;  D,  the  root;  E,  the  apex. 


Fig.  133 


Fig. 

128. 

Fig. 

129. 

Fig. 

130. 

Fig. 

I3I-- 

Fig. 

132. 

Fig. 

I33-- 

• 


@ 


Black's  figures  are:  Average  length  of  crown,  0.29;  of  root,  0.55; 
total,  0.84  inch. 

(&)  The  Crown. — (i)  The  Labial  Surface  is  convex  in  both  direc- 
tions, but  not  so  much  as  in  the  first  premolar.  It  is  widest  across 
the  middle  portion  of  its  surface.  The  upper  border  is  less  curved 
than  in  the  former.     The  cusps  are  more  equal  in  their  dimensions. 

The  convexity  of  the  {ii)  Lingual  surface  is  marked;  the  borders 
and  angles  are  rounded. 

The  {iii)  Mesial  and  (iv)  Distal  surfaces  are  not  parallel,  but  have 
a  tendency  to  slope  upwards  towards  the  root. 


THE  MAXILLARY  SERIES  191 

The  {v)  Morsal  surface  closely  resembles  that  of  the  first  premolar. 
In  fact,  it  is  often  extremely  difficult  to  determine  the  difference 
between  the  two,  on  regarding  the  masticating  surface  alone.  The 
elevation  of  the  cusps  is  nearly  identical.  The  labial  and  lingual  edges 
are  almost  of  the  same  size.  The  central  sulcus  is  less  deep  than  in  the 
first  premolar,  and  does  not  extend  so  far  forwards  or  backwards  as  in 
that  tooth. 

(c)  Neck. — The  Neck  is  practically  indistinguishable.  Its  situa- 
tion can,  however,  be  determined  by  the  position  of  the  free  margin 
of  the  enamel.  The  plane  occupied  by  the  cervical  margin  is  hori- 
zontal. 

{d)  Root. — The  Root  is  a  little  longer,  rather  smaller  and  more 
flattened  from  side  to  side  than  the  first  premolar.  It  may  be  bifur- 
cated and  possess  two  pulp  canals,  one  buccal  and  one  lingual.  It  is 
straight,  and  is  always  in  immediate  relationship  wnth  the  floor  of  the 
antrum  of  Highmore,  frequently  piercing  it.  The  anterior  groove 
is  often  absent,  and  it  is  generally  less  conspicuous  than  that  on  the 
distal  aspect. 

(e)  Calcification. — Calcification  begins  during  the  fifth  year  after 
birth,  and  is  superficially  completed  by  the  eleventh  or  twelfth.  The 
tooth  begins  to  erupt  about  the  tenth  year  and  third  month. 

(/)  Pulp  Chamber. — The  Pulp  Chamber  is,  in  outline,  similar  to 
that  of  the  tooth  itself.  The  cornua  are  less  accentuated  than  those 
of  the  first  premolar.  The  root  canal  is  single,  as  a  rule,  and  very 
flattened  from  side  to  side.  If  two  root  canals  exist  they  may  termi- 
nate by  a  common  apical  foramen. 

(g)  Identification. — Identification  is  not  always  easy  from  a 
miscellaneous  collection  of  teeth.  If  the  premolar  is  small,  has  very 
rounded  margins  to  its  crown,  and  if  the  central  coronal  sulcus  is 
short,  and  does  not  extend  to  the  mesial  and  distal  borders,  a  second 
maxillary  premolar  is  indicated.  It  is  practically  impossible  to  deter- 
mine whether  it  has  been  implanted  in  the  right  or  left  maxillary  bone. 

(//)  Surgical  Anatomy. — Its  anatomical  relationship  with  the 
antrum  is  most  important;  antrotomy  by  the  oral  route  may  be  per- 
formed through  the  socket.  According  to  Sir  John  Tomes,  it  is  the 
victim  of  caries  in  about  17  per  cent,  of  cases.     Black's  figures  are: 


192  THE  ANATOMY  OF   THE  TEETH  OF  MAN 

Mesial,  i6.i;  Distal,  17;  Labial,  4;  Lingual,  10.2;  Morsal,  6.7.  In 
France,  the  proportion  is  said  to  be  8  per  cent. 

In  opening  up  the  pulp  chamber  the  site  for  election  is  the  centre 
of  the  morsal  sulcus. 

The  Permanent  Molars. — The  word  "molar"  is  derived  from  Molar  is, 
a  millstone,  a  term  which,  particularly  appropriately,  expresses  its 
function  in  the  mouth  of  Man.  Molars  differ  in  shape,  size,  and 
external  configuration  and  volume  from  all  the  other  teeth.  The 
largest  of  all  the  dental  organs  of  Man,  they  occupy  the  posterior 
portions  of  the  dental  arch.  There  are  three  in  each  maxilla,  and 
three  on  each  side  of  the  mandible,  and  thus,  in  typical  circumstances, 
are  twelve  in  number.  They  are  the  sixth,  seventh,  and  eighth  teeth 
from  the  midline,  and  are  called  "first,"  "second,"  and  "third"  respec- 
tively. Clinically  they  are  designated  the  "six-year-old"  molar, 
the  "twelve-year-old  molar,"  and  the  "wisdom  tooth."  Regarding 
the  first  named,  this  nomenclature  is  far  from  being  correct,  and 
should  be  abolished.  For  the  "six-year-old"  molar  may  erupt  at  any 
age  between  four  and  eight  years,  the  "twelve-year-old"  tooth  from 
ten  to  fourteen,  while  the  "wisdom"  tooth,  or  dens  sapientice  of  the 
older  writers,  often  appears  long  before,  and  long  after,  the  epoch  of 
wisdom  has  arrived,  if  ever  it  does  arrive.  The  third  molars  some- 
times never  do  erupt,  and  it  would  be  well  for  the  civilized  races  of 
mankind,  if  it  did  disappear  entirely  from  their  dental  category.  The 
reader  is,  therefore,  strongly  advised  to  cultivate  the  faculty  of  naming 
the  molars  according  to  their  numerical  and  not  according  to  their 
popular  designations. 

These  teeth  come  into  the  dental  arches  behind  the  milk  teeth, 
and  have  no  predecessors,  being  derived  from  the  extension  back- 
wards of  the  Zahnleiste,  which  has  already  been  concerned  in  the  forma- 
tion of  the  forty  anterior  deciduous  and  permanent  enamel  organs. 

The  First  Right  Maxillary  Permanent  Molar. — This  tooth  is  probably 
of  greater  value  in  the  human  mouth  than  the  canine,  which  depends 
on  its  importance  as  an  aesthetic  addition  to  the  face.  On  account 
of  its  large  size  and  its  position,  about  midway  between  the  extremities 
of  the  dental  arch,  its  offices  are  more  purely  of  a  mechanical  nature 
than  the  other  teeth. 


THE  MAXILLARY  SERIES  193 

Black  would  attribute  to  the  first  molar  certain  special  functions, 
which  are  of  the  utmost  importance  before  the  shedding  of  the  decid- 
uous teeth,  and  often  prevent  distortion  of  the  features. 

He  writes*  (page  263) :  "In  the  examination  of  a  considerable  number 
of  cases  it  is  found  that  with  the  effect  of  disease  and  the  irregularities 
that  occur  in  the  absorption  of  the  roots  of  the  deciduous  teeth,  and 
their  replacement  by  the  permanent  teeth,  the  support  of  the  jaws 
is  many  times  almost  completely  lost,  but  for  the  presence  of  the 
first  molars.  They  do  much  more  than  this.  Accompanying  the 
shedding  process,  there  is  a  rapid  growth  of  the  bones  of  the  jaws  and 
face,  making  for  the  changes  of  the  features,  from  the  form  in  the  child 
and  the  modelling  of  the  features  of  the  adult.  Particularly  the  space 
from  the  lower  orbital  ridge  to  the  crest  of  the  alveolar  process,  between 
the  teeth  is  increasing,  the  depth  of  the  lower  jaw  from  the  crest  of 
the  alveolar  process  to  its  lower  border  is  increasing.  Together  these 
are  lengthening  the  face  from  above  downwards.  .  .  .  The  forma- 
tion of  the  first  molars  (is)  not  alone  in  holding  the  jaws  in  their  proper 
relative  positions,  while  the  occlusion  is  broken  up  in  the  shedding 
process,  but  they  also,  by  their  movement  in  harmony  with  the  general 
growth  of  the  face,  carry  the  jaws  further  apart,  and  in  this  way  assist 
in  the  formation  of  the  features  by  lengthening  the  face." 

Around  it  centres  most  discussion.  Its  orthodontical  value  cannot 
be  overestimated;  the  loss  sustained  by  the  dental  arches,  superior 
and  inferior,  as  a  consequence  of  its  removal,  premature  or  otherwise, 
is  enormous,  and  may  be  compared  to  the  breaking  of  the  sequence 
of  bricks  in  an  archway  by  the  displacement  of  the  "key-stone."  Its 
apparent  inability  to  ward  off^  early  attacks  of  caries  in  European 
mouths,  and  its  homological  significance,  go  to  render  this  tooth  the 
most  interesting  of  the  teeth  of  Man.  It  figures  largely  in  palaeontology, 
and  other  abstruse  sciences,  also  because  unlike  the  anterior  teeth, 
it  with  its  congeners  often  remains  more  firmly  implanted  in  the  jaws 
than  the  others,  and  is,  on  this  account,  useful  in  studying  the  dental 
characteristics  of  many  skulls  of  animals  and  even  prehistoric  JNIan. 
The  single-rooted  teeth  fall  out  of  their  sockets  in  the  dried  skull, 
but  the  triple-rooted  teeth  are  frequently  retained. 

The  anatomy  of  this  tooth  may  be  conveniently  considered  under 
13 


194  THE  ANATOMY  OF  THE  TEETH  OF  MAN 

the  following  headings:  (a)  Its  Mean  Measurements;  {b)  its  Crown; 
(c)  Neck;  {d)  Roots;  (e)  Calcification;  (/)  Pulp  cavity;  (g)  Identifi- 
cation; and  {h)  its  Surgical  Anatomy. 

(a)  Mean  Measurements. — From  the  apex  of  the  palatine  root 
to  the  free  margin  of  the  ridge  of  enamel  on  the  inner  border  of  the 
crown  the  length  is  22  mm.;  of  the  anterior  buccal  root  and  anterior 
portion  of  the  internal  border,  21  mm.;  of  the  posterior  buccal  root, 
and  the  posterior  part  of  the  external  border,  19  mm.  Black's  figures 
are  as  follow:  Average  length  of  crown,  0.30;  of  root,  0.51;  over  all, 
0.81  inch. 

Variations  of  Mensuration. — From  the  apex  of  the  anterior  buccal 
root  to  the  coronal  edge,  29  mm.,  and  11  mm.  across  the  crown  in  a 
mesio-distal  direction  for  the  largest,  and  10  mm.  by  4.5  mm.  for  the 
smallest  examined. 

{b)  Crown. — The  Crown  is  large  and  conical  in  shape,  the  buccal 
and  lingual  surfaces  rounder  than  the  mesial  and  distal.  There  are 
five  surfaces:  (i)  The  Buccal,  or  outer,  convex  in  both  directions, 
roughly  measures  twice  the  length  of  the  second  premolar.  Quadri- 
lateral in  outline,  and  most  constant  of  all  molars  in  its  general  pattern, 
it  is  narrower  above  than  below,  that  is,  the  lower  angles  spread  out 
and  become  very  rounded.  Midway  between  its  anterior  and  posterior 
borders  a  groove  is  formed  passing  from  above  downwards,  and  divid- 
ing it  into  two  nearly  equal  parts,  of  which  the  anterior  is  the  more 
protuberant.  This  groove  begins  at  a  spot  2  or  3  mm.  below  the  necks 
of  the  tooth.  The  lower  border  possesses  two  curves,  the  convexities 
of  which  look  downwards,  the  curves  themselves  representing  the  outer 
parts  of  the  two  external  cusps. 

{ii)  The  Palatine  or  inner  surface  is  more  irregular  in  outline  than 
the  buccal;  it  is  also  more  rounded.  Like  the  former,  it  is  narrower 
at  the  neck  of  the  tooth  than  elsewhere,  swelling  out  to  its  lowest 
edge  in  graceful  curves.  It  is  convex  in  both  dimensions.  Its  surface 
is  unequally  divided  into  two  parts  by  a  similar  groove  to  that  which 
obtains  on  the  buccal  side.  In  this  instance,  however,  while  starting 
at  about  a  similar  spot  near  the  neck,  it  passes  downwards  and  back- 
wards, and  makes  the  anterior  part  by  far  the  larger  of  the  two.  The 
curves  of  this  surface  are  not  so  clear  as  are  those  of  the  buccal  surface. 


THE  MAXILLARY  SERIES  195 

{in)  Mesially  the  crown  presents  a  horizontally-placed  rhomboid, 
which  is  very  slightly  convex,  and  of  which  the  upper  and  lower  borders 
are  nearly  parallel.  The  straightness  of  the  lower  border  is  due  to 
the  depression  between  the  antero-internal  and  the  antero-external 
cusps,  and  is  insignificant.  At  times  a  trifling  depression  is  seen  on 
this  surface. 

(«0  Distally  the  quadrilateral  character  of  the  anterior  surface 
is  well  maintained.  It  is  equally  flattened  and  equally  oblong  in  shape. 
But  the  lower  border  is  more  deeply  grooved  than  on  the  former  side. 

Fig.  134       Fig.  135     Fig.  136       Fig.  137       Fig.  138        Fig.  139 

WAV   •    A    fii . 


-The  maxillary  first  molar — Mesial  aspect.      X  \- 

-The  same — Buccal  aspect. 

-The  same — Lingual  aspect. 
■. — The  same — Bucco-lingual  section. 
I. — The  same — Mesio-distal  section. 

I. — The  same — Various  horizontal  sections:     .4,  through  the  crown;    5,  the 
neck;    C,  the  mid-portion;  D,  the  roots;  £,  near  the  apices  of  the  roots. 


Fig. 

134- 

Fig. 

135- 

Fig. 

136. 

Fig. 

I37-- 

Fig. 

138. 

Fig. 

I39-- 

o 


{v)  The  Morsal  Surface  is  the  most  interesting  of  all.  Around  the 
morphology  and  evolution  of  its  cusps  has  been  waged  much  polemical 
warfare.  Many  years  of  research  have  been  spent  in  attempting  to 
ascertain  and  explain  the  homologies  of  its  cusps,  and  to  substantiate 
the  claims  of  the  varied  and  various  arguments  and  deductions  brought 
forward  by  different  zoologists  and  palaeontologists  in  the  matter. 

It  presents  the  outlines  of  a  quadrilateral  figure  with  rounded  angles, 
and    surmounted — at    each    angle — by    prominent    elevations.      The 


196  THE  ANATOMY  OF   THE  TEETH  OF  MAX 

buccal  tubercles  or  cusps  are,  on  the  whole,  shorter  than  the  others — 
and  this  fact  enables  the  anatomist  to  establish  a  difference  between 
this,  and  the  second,  and  third  molars.  The  palatine  border  of  this 
surface  is  longer  than  the  same  border  on  the  morsal  surface  of  the 
second  or  third  molar,  another  point  which  seems  to  distinguish  this 
tooth,  whilst  a  third  distinguishing  feature  lies  in  the  fact  that  the 
palatine  border  of  the  second  molar  is  a  great  deal  more  rounded  off 
than  the  sharper  border  of  the  first. 

There  are  four  cusps,  an  antero-internal  or  inner  mesial,  an  antero- 
external  or  outer  mesial,  a  postero-internal  or  inner  distal,  and  a  postero- 
external or  outer  distal,  the  first  and  last  being  more  or  less  connected 
by  a  highly  accentuated,  unmistakable,  strong,  broad,  prominent  ridge 
of  enamel,  the  others  being  separated  by  deep  fossae. 

Of  the  four  cusps  the  largest  is  the  antero-internal.  It  is  the  homo- 
logue  of  the  protocone.  It  is  joined  to  the  postero-external  cusp  by  a 
marked  oblique  enamel  ridge,  and  is  found  in  the  anthropoid  ape. 
Occasionally  this  ridge  is  traversed  by  a  slight  fissure,  which  thus 
unites  the  anterior  and  posterior  fossae  of  the  crown.  The  lowest 
-part  of  this  cusp  is  the  most  prominent  part  of  the  tooth.  The  antero- 
external  cusp  is  joined  to  the  former  by  the  oblique  ridge  already 
described,  which  forms  the  lower  border  of  the  outer  surface. 

The  next  largest  cusp  is  the  antero-external,  the  smallest  the  postero- 
internal, which  is  separated  from  the  other  by  a  sulcus  which  passes 
from  within  backwards  and  sharply  outwards.  The  postero-external 
cusp  is  the  homologue  of  the  metacone,  the  postero-internal  of  the 
hypocone,  and  the  antero-external  of  the  paracone.  An  extra,  a  fifth 
cusp,  is  often  developed  over  the  antero-internal  cusp  of  this  tooth. 

(c)  Neck. — The  Neck  of  the  first  permanent  molar  is,  on  hori- 
zontal section,  rhomboidal  in  outline,  larger  on  the  palatine  than  on 
the  buccal  aspect.  It  occupies  a  horizontal  plane,  the  amelo-cemental 
junction  being  very  indistinct.     {Cf.  the  Deciduous  Molars.) 

{d)  Roots. — There  are  three  roots,  of  which  one  is  placed  internally, 
the  palatine,  and  two  externally,  the  anterior  and  posterior  buccal. 
Of  these,  the  latter  is  flattened  from  side  to  side,  the  posterior  is  shorter 
than  the  anterior  and  generally  somewhat  straighter,  and  the  anterior 
frequently  inclined  to  be  grooved,  and  become  cur\-ed  in  a  backward 


THE  MAXILLARY  SERIES  197 

direction.  Seen  from  the  anterior  point  of  view,  the  latter  more  closely 
approaches  the  outlines  of  an  isosceles  triangle  than  the  former,  which 
is  altogether  a  smaller  root.  The  most  important  of  the  three,  and 
the  most  divergent,  thereby  ensuring  great  strength  to  the  implanta- 
tion of  this  tooth,  is  the  palatine  root,  which  passes  inwards  towards 
the  palate,  from  the  junction  of  the  bases  of  the  two  buccal  roots  with 
the  cervical  region  of  the  tooth.  It  is  much  more  cylindrical  in  shape 
than  the  others  but  still  is  rather  flattened  from  without  inwards. 
It  is  frequently  twisted  and  its  apical  region  deflected  gently. 

Occasionally  the  buccal  roots  become  fused  together,  and  occasionally 
the  buccal  and  the  palatine.  All  three  roots  may  communicate  with 
the  antrum,   particularly  the  palatine. 

{e)  Calcification. — Calcification  of  this  tooth  begins  before  any 
of  the  other  of  the  permanent  series.  This  is  a  very  important  point. 
The  earliest  signs  of  its  development  of  dentine  and  enamel  of  the 
cusps  in  Man  have  been  observed  about  the  eighth  month  of  intra- 
uterine life.  The  hard  parts  are  superficially  completed  by  the  ninth 
or  tenth  year,  and  the  tooth  is  erupted  from  the  sixth  to  the  sixth  year 
and  sixth  month  (28  per  cent.). 

(/)  Pulp  Cavity. — The  general  shape  of  the  Pulp  Cavity  and  the 
root  canals  can  be  ascertained  from  Figs.  137,  138,  and  151.  The  cornua 
follow  closely  the  shape  and  positions  of  the  cusps,  the  whole  pulp 
chamber  that  of  the  crowns.  At  its  base  there  is  an  infundibulum 
whence  arise  the  three  radicular  canals.  Their  calibres  diminish  very 
rapidl}'  to  the  apical  foramina.  The  buccal  canals  are  exceedingly 
flattened  from  side  to  side,  that  of  the  palatine  is  generally  cylindrical. 

(g)  Identification. — Identification  is  easy.  If  the  palatine  root 
is  held  between  the  thumb  and  index  finger  of  the  left  hand  and  the 
crown  is  directed  upwards,  the  end  of  the  oblique  ridge  of  enamel  which 
is  nearest  to  the  spectator  points  to  the  side  to  which  the  tooth  belongs. 

Qi)  Surgical  Anatomy. — The  general  length  of  the  palatine  root  is 
half  an  inch.  The  anterior  buccal  is  I  to  tV,  and  the  posterior  buccal 
t  inch.  The  entrance  to  the  posterior  buccal  root  is  frequently  obliter- 
ated. Externally,  tartar  is  commonly  present  on  the  buccal  surface  of 
the  crown,  owing,  no  doubt,  to  its  proximity  to  the  orifice  of  Stenson's 
duct,  and  beneath  the  gum  margin,  enamel  nodules  are  often  formed 


198 


THE  ANATOMY  OF   THE  TEETH  OF  MAN 


Fig.  140 


between  the  two  buccal  roots.  The  pulp  chamber  is  roughly  triangular 
in  shape.  It  should  be  opened  up  thoroughly,  to  expose  well  the 
entrance  to  the  canals. 

When  extracting  this  tooth,  the  forceps  blades  should  be  made 
to  grasp  the  circumference  of  the  palatine  root  internally,  and  the 
space  between  the  buccal  roots  externally.  It  is  very  frequently  an 
oblique-rooted  tooth,  due  to  the  fact  that  the  posterior  buccal  root 
lies  internally  to  its  normal  position.  If  it  possess  a  crown  of  which 
the  obliquity  is  noticeable,  it  may  be  surmised  that  the  position  and 
shape  and  general  character  of  the  roots  is  irregular  also.    The  anterior 

buccal  root  is  in  close  connection  with  the 
floor  of  the  antrum.  It  is  the  earliest  per- 
manent tooth  to  erupt,  and  is  said,  in 
Europe,  to  be  the  first  to  "decay."  Hence, 
special  care  should  be  exercised  in  cleans- 
ing it. 

In  orthodontics.  Angle's  system  of  classi- 
fication is  often  adopted  regarding  the 
occlusion  of  this  tooth  with  the  opposing 
mandibular  first  and  second  molars.  Ab- 
scess in  the  hard  palate  is  produced  by 
suppuration  occurring  in  the  palatine  root, 
abscess  in  the  vestibuliim  oris  from  the 
buccal  roots. 

The  frequency  of  the  occurrence  of  caries  in  this  tooth  appears  to 
differ  in  different  countries. 

In  Great  Britain  it  is  clinically  believed  that  the  first  permanent 
molar  is  the  most  frequently  carious. 

Out  of  2628  cases  of  extractions,  on  account  of  carles  and  its  conse- 
quences noted  by  Sir  John  Tomes,  the  first  molars  numbered  1090. 
Magitot"  out  of  10,000  cases  gave  the  number  as  15.4  per  cent. 
(the  mandibular  first  permanent  molar  18  per  cent.),  while  Black 
has  noted  in  a  hundred  persons  the  following:  Caries  of  the  mesial 
surface,  16;  distal,  6.2;  buccal,  1.2;  palatine,  o.i;  morsal,  24  (i.  e., 
the  fourth  position  most  frequently  observed  in  the  maxillary  series,  the 
others  being  mesial  surface  of  the  first  incisor,  31.6;  mesial  surface  of 


Bucco-lingual  section  through  a 
maxillary  molar  in  situ,  to  show 
its  osseous  relationships.     X  \. 


THE  MAXILLARY  SERIES  199 

the  second  incisor,  28;  distal  surface  of  the  first  incisor,  26.3,  and  the 
morsai  surface  of  the  maxillary  first  molar).  According  to  Mr.  J.  G. 
Turner,  dental  cysts  arise  in  connexion  with  this  tooth  more  than 
any  other  in  the  proportion  of  47  to  100. 

The  Second  Right  Maxillary  Permanent  Molar. — This  tooth,  the 
so-called  "twelve-year-old"  molar,  is  the  last  tooth  but  one  in  the 
maxilla,  and  usually  begins  to  make  its  way  into  the  dental  arch 
behind  the  first  permanent  molar  after  the  canine  and  second  pre- 
molar are  already  in  place. 

(a)  Mean  Measurements. — Extreme  length  from  apex  of  palatine 
root  to  the  most  prominent  part  of  the  antero-internal  cusp  is  22  mm. 
Extreme  width  across  the  broad  mesial  surface  11  mm.  Black's 
measurements  are:  Average  length  of  crown,  0.28;  of  root,  0.5;  length 
over  all,  0.79  inch. 

J'ariatioiis  of  Meusiiratiou. — Length,  24  mm.  to  29  nmi.;  width, 
10  mm.  to  12  mm. 

{b)  Crown. — The  Crown  is  smaller,  more  inclined  to  be  triangular, 
and  more  rounded  generally  than  that  of  the  first  molar,  otherwise  its 
external  configuration  closely  follows  it. 

Of  the  (?)  Mesial  and  («')  Distal  surfaces,  both  more  convex  and  not 
so  flattened  as  in  the  first  molar,  the  former  is  somewhat  broader  than 
the  latter,  and  shelves  off,  on  the  internal  side,  to  form  the  prominence 
of  the  antero-internal  cusp,  of  which  the  free  extremity  is  the  lowest 
part  of  the  crown.  The  Distal  is  more  convex  than  the  mesial  surface, 
and  rounder,  its  lower  border  of  equal  size,  that  is,  the  extremities  of 
the  cusps  are  about  the  same  length. 

{i'ii)  The  Buccal  surface  is  like  that  of  the  first  molar,  but  shelves 
off  towards  the  distal  part,  and  the  grooving  is  not  extensive,  but 
marked  at  the  lower  border. 

{iv)  The  Palatine  surface  is  exceedingly  convex,  slopes  up  to  the 
extremity  of  the  antero-internal  cusp,  and  the  groove  seen  on  the 
corresponding  surface  of  the  first  molar  is  here  suppressed.  The 
distal  portion  of  this  surface  may  be  much  diminished  in  size.  In 
many  specimens,  this  fourth  cusp  (the  postero-internal)  is  diminutive 
or  even  wanting. 


200 


THE  ANATOMY  OF   THE  TEETH  OF  MAN 


(v)  Morsal  Surface. — The  largest  cusp  is  the  antero-internal  joined 
to  the  postero-external  by  an  obhque  ridge  which  is  traversed  by  a 
sHght  sulcus.  There  are  two  deep  fossae  present,  one — anterior — is 
situated  behind  the  oblique  ridge,  and  the  antero-external  cusp,  and 
divides  into  a  fissure  running  between  the  two  external  cusps,  and 
another  running  between  the  two  anterior  cusps;  and  the  other — 
posterior — lying  behind  the  middle  part  of  the  oblique  ridge,  and 
sending  a  prolongation  or  fissure  inwards  and  forwards  to  divide  the 
postero-  and  antero-internal  cusps  from  each  other. 


Fig.  141       Fig.  142      F.'g.  143     Fig.  144      Fig.  145      Fig.  146 


v 


Fig.  141 
Fig.  142 
Fig.  143 
Fig.  144, 
Fig.  145 
Fig.  146, 


— The  maxillary  second  molar — Mesial  aspect.     X  t-  r^\\ 

— The  same — Distal  aspect.  V^ft* 

— The  same — Buccal  aspect.  |  ^\ 
— The  same — Bucco-lingual  section. 

— The  same — Mesio-distal  section.  fS  Q 

The  same — Various  horizontal  sections:     A,  through  the  crown:    B,  the      ^ 


neck;   C,  the  neck;  D,  mid-portion;  E,  the  roots;  F,  the  apices. 


•f 


(c)  Neck. — The  Neck  is  irregular  in  outline  and  circumference, 
and  is  simply  marked  by  an  annular  depression. 

{d)  Roots. — The  Roots  are  three  in  number,  are  not  so  divergent 
as  in  the  first  molar,  and  are  generally  curved  in  a  distal  direction. 
Sometimes  there  is  fusion  of  all  the  roots,  with  grooves  indicating 
their  probable  outlines.  Often  the  palatine  and  anterior  buccal  roots 
are  confluent,  rarely  the  palatine  and  the  posterior  buccal. 


THE  MAXILLARY  SERIES  201 

{e)  Calcification. — Calcification  begins  about  the  fifth  year,  and 
is  completed  from  the  sixteenth  to  the  eighteenth  year.  The  tooth 
begins  to  erupt  about  the  eleventh  year  and  ninth  month. 

(/)  Pulp  Cavity  and  Root  Canals.  —  In  shape  the  former 
is  oblong  from  the  buccal  to  the  palatine  side,  the  cornua  are 
not  so  very  marked,  and  the  floor  of  the  cavity  is  rounded,  or 
almost  flat.  With  regard  to  the  latter,  the  canals  are  shorter  and 
very  much  more  flattened  laterally  than  those  possessed  by  the 
first   molar. 

{g)  Identification. — Identification  of  this  tooth  is  not  difficult, 
the  salient  features  being  the  rounded  character  of  the  edge  of  the 
crown  over  the  palatine  root.  If  the  palatine  root  is  held  by  the  thumb 
and  index  finger  of  the  left  hand,  and  the  crown  of  the  tooth  is  upper- 
most, the  end  of  the  oblique  ridge  nearest  the  spectator  points  to  the 
side  to  which  it  belongs. 

{h)  Surgical  Anatomy. — As  the  external  alveolar  plate  is  here 
very  thin,  in  the  operation  of  extraction,  traction  on  the  tooth  should 
be  directed  outwards  towards  the  cheek.  In  the  performance  of  al\-eolar 
antrotomj^  for  empycemi  antri  it  is  often  convenient  and  expedient 
that  the  trochar  be  made  to  penetrate  the  upper  extremity  of  the 
socket  of  the  palatine  root. 

The  Third  Right  Maxillary  Permanent  Molar. — This  tooth  is  the 
most  variable  in  size,  shape,  position,  and  character  of  crown  and 
roots  of  any  of  the  other  molars.  It  possesses  a  great  variety  in  the 
morphology  of  the  crown,  two  specimens  scarcely  ever  being  identical. 
While  the  second  molar  somewhat  resembles  the  first,  the  third  bears 
only  a  superficial  likeness  to  the  second.  It  is  the  smallest  of  the  three, 
and  is  often  tri-cuspidate. 

(a)  Mean  Measurements. — Extreme  length  from  the  apex  of  the 
anterior  buccal  root  to  the  most  prominent  part  of  the  interno-external 
cusp  is  20  mm.;  extreme  width  of  mesial  surface,  ii  mm.  Black's 
figures:  Average  length  of  crown,  0.24;  of  root,  0.44;  length  over  all, 
0.65  inch. 

Variations  of  lilcnsiiration. — The  smallest  examined  was  10  mm. 
long  and  4.5  broad  in  the  same  situations. 


202  THE  ANATOMY  OF   THE  TEETH  OF  MAN 

{b)  Crown. — (i)  The  Mesial  surface  is  very  flat  and  broad,  there  is 
no  cervical  prominence  or  limit,  the  whole  front  surface  sloping  grad- 
ually upward  from  the  lower  border  to  the  roots. 

(ii)  The  Distal  surface  is  extremely  rounded,  convex,  and  short. 
The  amelo-cemental  junction  is  inconspicuous,  but  occasionally  some- 
what grooved.  If  a  fourth  cusp  is  present  the  highest  part  of  the 
tooth  is  the  buccal  side  of  the  lower  border  of  the  distal  surface.  If 
three  cusps  are  present,  the  internal  cusp  is  the  highest.  All  the 
angles  are  very  rounded. 

(Hi)  The  Buccal  surface  is  identical  with  that  of  the  first  and  second 
molars,  but  generally  shorter  and  rather  more  convex.  A  slight  vertical 
groove  may  exist  on  the  lower  border. 


Fig.  147  Fig.  148  Fig,  149  Fig.  150 


Fig.  147. — The  maxillary  third  molar — 
Mesial  aspect.      X  t- 

Fig.  148. — The  same — Distal  aspect. 

Fig.  149. — The  same — Buccal  aspect. 

Fig.  150. — The  same  —  Mesio-distal 
section. 


» 


(iv)  The  Palatine  surface  is  very  narrow  antero-posteriorly,  very 
convex,  and  not  grooved.  Its  highest  part  corresponds  to  the  antero- 
internal  cusp  of  the  first  or  second  molar. 

iv)  The  Morsal  surface:  Of  the  cusps,  the  postero-internal  is  the 
smallest,  and  in  many — perhaps  most — instances  is  entirely  sup- 
pressed. Probably  50  per  cent,  of  these  teeth  have  no  fourth  cusp. 
The  internal  cusp  is  very  large  in  the  tri-cuspidate  teeth,  and  a  deep 
fossa  is  formed  in  the  middle  of  the  crown  and  extends  outwards  as  a 
fissure,  between  the  two  external  cusps,  often  sending  a  smaller  fissure 
backwards  to  separate  the  postero-external  from  the  large  palatine 
cusp.  The  oblique  ridge,  therefore,  is  absent  in  these  tri-cuspidate 
teeth,  and  now  serves  to  constitute  the  distal  ridge  running  along 
the  lower  border  from  without  inwards. 

(c)  Neck. — The  Neck  is  oblong  from  without  inwards.  Its  mark- 
ings are  absent  in  front,  but  are  more  or  less  visible  behind. 

{d)  Roots. — The  maxillary  third  molar  possesses  three  roots,  two 
buccal  and  one  palatine,  like  the  first  and  second  molars.     Many  have 


THE  MAXILLARY  SERIES 


203 


their  roots  all  convergent,  some  develop  four,  five,  or  six  roots.  In 
these  instances  the  neck  is  very  much  compressed  from  side  to  side, 
and  the  crown  most  irregular  in  outline,  shape,  and  size.  The  roots 
are  smaller  and  slenderer  than  those  of  the  second  molar,  the  palatine 
being  at  times  even  the  smallest  of  the  three.  When  three  cusps  only 
exist,  the  outer  two  are  frequently  confluent. 


Fig   151 


Horizontal  sections  through  the  alveolar  process  of  the  right  maxilla  of  an  adult  with  the  perma- 
nent teeth  in  situ.  X  f.  A,a.t  the  gingival  margin  of  the  bone;  B,  at  the  root  portions  of  the 
teeth.    The  shapes,  sizes,  and  positions  of  the  pulp  cavities  and  root  canals  are  by  no  means  constant. 

(e)  Calcification. — Calcification  begins  about  the  ninth  year,  is 
superficially  completed  from  the  eighteenth  to  the  twentieth  year  and 
the  tooth  may  erupt  from  the  seventeenth  to  the  twentieth  year.  It, 
however,  is  often  not  erupted  till  middle  age. 


204  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

if)  Pulp  Cavity  and  Root  Canals. — The  outlines  of  the  Pulp 
Cavity  and  Root  Canals  are  very  varied  and  difficult  to  describe. 
The  pulp  chamber  is  usually  triangular,  the  outer  side  being  the  short- 
est of  the  three.  The  cornua  are  not  pronounced.  The  orifices  of  the 
root  canals  are  closer  together  than  obtains  elsewhere,  and  are  very 
small.  If  the  tooth  has  a  single  root,  one  pulp  chamber  only  may 
exist,  the  floor  of  the  pulp  cavity  which  is  seen  in  the  other  molars 
being   absent. 

(g)  Identification. — Identification  can  be  mainly  effected  by  the 
size,  and  slenderness  of  the  roots,  and  the  elimination  of  the  characters 
of  the  other  molars.  If  three  cusped,  then  the  tooth  is  the  maxillary 
third  molar.  If  the  palatine  root  is  well  formed,  and  is  held  as  described 
in  a  previous  page,  the  flattened  mesial  surface  of  the  crown  points 
to  the  side  to  which  the  tooth  belongs. 

{h)  Surgical  Anatomy. — The  full  formation  of  the  apical  region 
of  this  tooth  occurs  about  the  time  of  eruption,  a  point  worthy  of 
notice  when  extirpation  of  the  pulp,  and  filling  of  the  root  canals  are 
required.     It  is  frequently  impacted  and  misplaced.      (See  Fig.  201.) 


THE    MANDIBULAR    SERIES 

The  Incisors. — The  main  differences  between  the  maxillary  and 
mandibular  incisors  lies  in  the  size.  Comparison  of  specimens  of 
each,  reveals  the  fact  that  the  architecture  of  the  latter,  although 
founded  on  general  similar  lines  is  more  refined  and  graceful  than 
the  former.  The  teeth' taper  most  gradually  from  the  incisive  edge 
to  the  radicular  apex.  The  two  first  incisors  maxillary  and  mandibular 
— are  the  most  dissimilar;  the  two  second  more  closely  match  each 
other.  Another  salient  point  is  that  the  cingulum,  which  is  often 
enlarged  and  overdeveloped  in  the  upper  teeth,  is  usually  wholly 
wanting  in  the  lower;  the  appearance  of  a  lingual  cusp  being  probably 
entirely  unknown  in  this  situation. 

The  First  Right  Mandibular  Permanent  Incisor. — The  smallest 
tooth  of  all,  it  is  placed  in  the  front  of  the  mandible  immediately  to 
the  right  of  the  central  line,  the  mandibular  "incisive  spot."     It  bears 


THE  MANDIBULAR  SERIES  205 

the  same  relationship  with  regard  to  its  mesial  surface  to  the  ver- 
tical line  passing  through  the  middle  of  the  face  (that  in  the  same 
direction  as  the  sagittal  suture  of  the  skull)  as  does  the  maxillary 
first  incisor. 

(a)  Mean  Measurements. — The  extreme  length  from  the  apex 
to  the  cutting  edge  is  23  mm.,  the  width  at  the  neck  being  6  mm. 
It  is  slightly  longer  in  the  mesial  than  on  the  distal  side.  Black's 
figures  are  as  follow:  Length  of  crown,  0.34;  of  root,  0.47;  over  all, 
0.81  inch. 

Variations  of  Measurement. — The  greatest  measures,  27.5  mm. 
long,  and  5.5  across  the  incisive  edge;  the  shortest  18  mm.,  and  3  mm. 
in  the  same  diameters. 

{b)  Crown. — The  Crown  is  cone-shaped,  the  cone  having  its  base 
compressed  from  side  to  side,  and  the  apex  (the  cutting  edge)  flattened, 
and  extended  from  before  backwards.  It  is  very  small,  and  presents 
fewer  irregularities  of  surface  and  conformation  than  the  correspond- 
ing upper  tooth.  It  is,  therefore,  much  more  constant  in  shape  and 
general  characteristics.  The  surfaces  are  labial,  lingual,  mesial,  and 
distal. 

(/)  Labial. — This  is  triangular,  with  the  blunt  apex  of  the  triangle 
pointing  downwards,  and  the  base  at  the  cutting  edge.  Convex  in 
both  directions,  its  angles  are  clearly  defined  and  both  acute.  At 
times  there  are  faint  traces  of  a  double  vertical  grooving,  which  is 
more  marked  at  the  edge  than  lower  down. 

(ii)  The  Lingual  surface  is  concave  in  both  planes,  but  more  pro- 
nounced in  a  mesio-distal  direction.  The  surface  here  is  also  triangular, 
the  apex  again  at  the  gingival  margin,  but  acuter  than  that  of  the 
opposite  surface. 

(m)  The  Mesial  aspect  is  verj-  flat,  triangular  in  outline,  having 
its  base  at  the  gingival  edge,  and  its  acute  apex  at  the  cutting  edge. 
The  amelo-cemental  junction  is  very  indistinct. 

(iv)  The  Distal  surface  is  also  triangular,  slighth'  concaA-e  from 
above  downwards,  and  slightly  convex  in  the  labio-lingual  direction. 
It  is  somewhat  shorter,  and  somewhat  smaller  than  that  on  the  oppo- 
site surface.  The  incisive  border  is  the  widest  part  of  the  tooth;  its 
angles  are  acute. 


206 


THE  ANATOMY  OF   THE  TEETH  OF  MAN 


(c)  Neck. — The  Neck  is  inconspicuous,  being  intimately  blended 
with  the  root. 

(d)  Root. — The  Root  is  long,  narrow  from  before  backwards,  and 
very  flattened  laterally.  Its  anterior  border  is  the  broader  of  the  two 
and  at  the  same  time  a  little  longer,  and  also  a  little  more  convex. 
The  posterior  border  is  thin  and  tapers  almost  to  a  point  at  its  apex. 
The  mesial  aspect  is  flat  from  above  downwards,  slightly  convex  from 
side  to  side,  and  possesses  no  groove.  The  distal  aspect  is  concave 
in  both  directions;  a  shallow  groove  runs  through  the  greatest  part 
of  its  length.     The  apical  foramen  is  indistinguishable. 


Fig.  152 


Fig.  153 


Fig.  154 


Fig.  155 


Fig.  156 


Fig.  157 


■\   B 


— The  mandibular  first  incisor — Labial  aspect.      X  x- 
— The  same — Lingual  aspect. 
— The  same — Mesial  aspect. 
— The  same — Mesio-distal  section. 
— The  same — Labio-lingual  section. 

— The  same — Various   horizontal   sections:      A,    through    the    crown;    B, 
through  the  crown;  C,  micf-portion;  D,  the  root;  E,  near  the  apex. 


Fig. 

152- 

Fig. 

153- 

Fig. 

I54-- 

Fig. 

155- 

Fig. 

156. 

Fig. 

I57-- 

(e)  Calcification. — Calcification  begins  during  the  first  year  post 
natum,  and  is  completed  during  the  tenth  year.  The  tooth  is  erupted 
midway  between  the  sixth  and  seventh  years  in  30.5  per  cent,  of  cases. 

(/)  Pulp. — The  Pulp  cavity  follows  very  uniformly  the  external 
configuration  of  the  tooth.  It  is  flattened  in  a  labio-lingual  direction, 
and  its  cornua  correspond  with  the  angles  of  its  cutting  edge.  It  is 
naturally  exceedingly  small  and  tube-like  in  the  radicular  region,  and 
at  times  may  even  be  bifurcated,  and  possess  two  small  flattened 
canals,  which,  however,  become  united  at  the  apex. 

(g)  Identification. — If  the  tooth  is  placed  in  a  horizontal  posi- 
tion with  the  apex  of  the  root  towards  the  observer  the  longest  side 
(i.  e.,  from  angle  to  apex)  is  on  the  side  to  which  the  tooth  belongs. 


THE  MANDIBULAR  SERIES  207 

{h)  Surgical  Anatomy. — Usually  age  changes,  such  as  translucency 
of  the  root,  occur  more  frequently  at  an  earlier  period  in  this  than  in 
the  second  incisor.  Hence,  of  all  the  incisors  of  the  lower  jaw,  it  is 
the  first  to  be  shed.  Another  common  age  change  is  that  of  the 
pigmentation,  in  a  mesio-distal  direction,  of  the  cutting  edge  of  this 
and  the  neighbouring  tooth.  It  may  be  ascribed  to  degeneration  and 
discolouration  of  the  pulp  which  have  stained  the  overlying  dentine. 

The  Second  Right  Mandibular  Permanent  Incisor. — This  bears  a 
strong  superficial  resemblance  to  that  just  described.  It  is,  however, 
larger,  has  a  broader  crown,  is  wider  at  the  cutting  edge,  and  has  a 
longer  root. 

(a)  Mean  Measurements. — Extreme  length,  24.5  mm.;  width 
at  cutting  edge,  6  mm.  Black's  measurements:  Average  length  of 
crown,  0.35;  front,  0.50;  over  all,  0.85  inch. 

Variations  of  Mensuration. — The  length  of  the  largest  was  27  mm.; 
width,  5.5  at  the  incisive  edge.  The  smallest  was  17  mm.  long  and 
5.5  wide. 

(&)  Crown. — The  Crown  is  more  fan-shaped  than  the  first  incisor. 
It  has  four  surfaces. 

{i)  The  Labial  side  is  triangular,  with  a  blunt  apex  directed  down- 
wards, being  slightly  convex  in  both  directions.  There  may  be  vestiges 
of  a  vertical  groove  in  the  centre  of  this  surface.  The  upper  border 
is  longer  than  that  of  the  first  incisor. 

(//')  Lingually  the  crown  is  very  concave  from  side  to  side,  and 
slightly  so  from  above  downwards,  terminating  at  the  neck,  in  a  small 
prominence,  which  reminds  the  student  of  an  attempt  at  an  elevation 
of  the  edges  of  the  cingulum.     No  pits  or  fissures  are  ever  seen  here. 

(m)  The  Mesial  surface  is  triangular,  having  its  base  below.  It 
is  slightly  concave.  Its  junction  with  the  neck  of  the  tooth  is  indis- 
tinguishable. 

(«')  The  Distal  triangular  surface  is  also  concave  in  both  directions. 

(c)  Neck. — The  Neck  is  inconspicuous  on  the  mesial  and  distal 
surfaces,  slightly  visible  on  the  labial,  but  more  marked  on  the  lingual 
side. 

(rf)  Root. — The  Root  is  similar  to  that  of  the  first  incisor,  but  both 
labial   and   lingual   aspects  are   more   inclined   to   be  of  equal   width. 


208 


THE  ANATOMY  OF   THE  TEETH  OF  MAN 


The  apex  is  acute.    It  is  more  grooved  distally  than  mesially.    Attempts 
at  the  formation  of  two  roots  often  occurs. 

{e)  Calcification. — Calcification  begins  the  first  year  after  birth, 
and  is  superficially  completed  from  the  tenth  to  the  eleventh.  The 
tooth  begins  to  erupt  in  28.5  per  cent,  of  cases,  about  the  seventh 
year  and  sixth  month. 


Fig.  158 


Fig  159 


Fig.  160 


» 


Fig.  162 


Fig.  163 


Fig.  164 


Fig. 

158 

Fig. 

159 

Fig. 

160 

Fig. 

161 

Fig. 

162 

Fig. 

163 

Fig. 

164 

X  -;. 


— The  mandibular  second  incisor — Labial  aspect. 
— The  same — Lingual  aspect. 
— The  same — Mesial  aspect. 
— The  same — Mesio-distal  section. 
— The  same — Mesio-distal  section  in  another  plane. 
— The  same — Labio-lingual  section. 

— The  same — Various  horizontal  sections;     A,  through  the  crown;  B,  the 
neck;   C,  mid-portion;  £>,  the  root;  E,  near  the  apex. 


(/)  Pulp  Chamber. — The  Pulp  chamber  and  root  canal  are  similar 
in  most  particulars  to  those  of  the  first  incisors;  the  latter  is  frequently 
bifurcated. 

{g)  Identification. — Identification  may  be  accomplished  by  the 
same  means  as  the  first  incisor.  A  large  mandibular  incisor  is  probably 
the  second. 

(g)  Surgical  Anatomy. — It  is  seldom  necessary  to  have  to  open 
up  the  pulp  chamber  of  this  tooth,  on  account  of  its  immunity  from 
the  attacks  of  dental  caries.  A  spot  on  the  lingual  side  of  the  cutting 
edge  centrally  placed  is,  however,  the  most  suitable  to  choose.  If 
the  tooth  has  become  abraded  as  an  old  age  change,  an  opening  must 
be  effected  through  the  cutting  edge,  and  the  direction  must  be  near 
the  labial  side. 

The  Right  Mandibular  Permanent  Canine. — The  mandibular  canine 
differs  but  little  from  the  upper  tooth,  the  main  point  being  the  size 


THE  MANDIBULAR  SERIES  209 

of  the  crown,  which  is  longer  in  the  former  than  in  the  latter.  The 
external  (labial)  outline  of  the  tooth,  moreover,  is  more  gently  curved 
from  cusp  to  apex  than  the  other,  being  modelled  on  the  shape  of  an 
arc  of  a  circle,  so  that  the  most  prominent  part  is  at  the  neck. 

(a)  Mean  Measurements. — Extreme  length,  31  mm.;  and  width, 
12  mm.  Black's  figures  are:  Length  of  crown,  0.40;  of  root,  0.60; 
over  all,  i  inch. 

Variations  of  Mensuration. — The  largest  examined  was  33.5  long, 
and  8  mm.  broad;  the  shortest,  22.5  long,  and  6  mm.  broad.* 

(6)  Crown. — The  Crown  is  cone-shaped  and  flattened  on  all  four 
sides,  but  more  on  the  labial  and  the  lingual  than  the  others.  Looked 
at  from  above,  the  labial  convexity  slopes  off,  on  account  of  the  larger 
area  occupied  by  the  mesial,  rather  than  the  lingual  surface,  thus 
presenting  the  outline  of  an  irregular  triangle  of  which  the  base  is 
directed  towards  the  midline  of  the  jaw.     It  has  four  surfaces. 

(?')  The  Labial  surface  is  convex  in  both  directions,  frequently- 
roughened  by  the  presence  of  horizontal  or  vertical  rows  of  shallow 
pits.  The  lower  border  is  rounded,  its  upper  pointed  border  (cutting 
edge)  terminates  at  an  excentric  spot  which  encroaches  on  the  right, 
so  that  the  cutting  edge,  running  from  the  extremity  of  the  cusp  for- 
wards to  the  mesial  angle,  is  shorter  than  that  running  backwards  to  the 
distal  angle.  A  slightly  raised  ridge  of  enamel  often  extends  down- 
wards, and  this  gives  to  the  surface  the  appearance  of  two  vertical 
shallow  grooves,  one  in  front  and  the  other  behind. 

{ii)  More  concave  from  side  to  side  than  from  abo\-e  downwards 
the  Lingual  surface  has  a  vertical  ridge  of  enamel  which  di\ides  it 
into  two  unequal  parts,  of  which  the  anterior  is  larger  than  the 
posterior. 

(///)  The  Mesial  surface  is  much  broader  than  the  distal,  in  shape 
like  a  blunt  triangle,  the  base  of  which,  on  the  level  of  the  gum  margin, 
is  encroached  upon  by  the  cementum.      Its  height  compared   to  its 

*  Rarely,  this  tooth  may  become  enormously  developed  and  assume  the  dimensions  of  the  inferior 
canine  of  the  anthropoid  ape.  A  celebrated  historical  instance  occurred  in  the  case  of  Geoffroy-la- 
Grand'Dent,  surnamed  Geoffroi  II,  of  the  House  of  Lusignan,  who,  as  a  puissant  noble  of  Poitou, 
flourished  in  the  Twelfth  Century.  He  was  so-called  because,  in  the  mediaeval  French  tongue,  as 
recorded  in  the  "Roman  de  Melusine,"  written  in  1387,  by  order  of  Charles  V,  "il  apporta  sur  terre, 
une  dent  qui  lui  yssoat  hors  de  la  bouche  plus  d'un  ponce. " 
14 


210  THE  ANATOMY  OF   THE  TEETH  OF  MAN 

width  is  remarkable,  as  the  mesial  cutting  edge  extends  some  distance 
on  to  it.     It  is  very  flat,  hardly  convex. 

(iv)  The  Distal  is  not  so  broad  as  the  former  surface;  it  is  more 
convex,  and  its  upper  part  is  thickened  by  the  prominent  termination 
of  the  distal  part  of  the  cutting  edge.  It  is  slightly  concave  both  ways, 
in  its  lower  part. 

(c)  Neck. — The  Neck  is  more  pronounced  on  the  labial  and  lingual 
sides  than  on  the  other  surfaces. 

Fig.  165  Fig.  166  Fig.  167  Fig.  168  Fig.  169  Fig.  170 


Fig. 

165. 

Fig. 

166. 

Fig. 

167. 

Fig. 

168. 

Fig. 

169. 

-The  mandibular  canine — Labial  aspect.     X  y- 
-The  same — Lingual  aspect. 
-The  same — Mesial  aspect. 
-The  same — Mesio-distal  section. 
-The  same — Labio-lingual  section. 
Fig.   170. — Various  horizontal   sections:    A,   through  the  crown;   B,   the   neck;  C, 
mid-portion;  D,  the  root. 

(d)  Root. — The  Root  is  long,  strong,  and  broad  at  the  gingival 
margin,  and  tapers  gradually  to  its  apex,  being  inclined  slightly  towards 
its  distal  aspect.  The  labial  is  broader  than  the  lingual  aspect,,  and 
the  mesial  slightly  narrower  than  the  distal.  Both  are  grooved,  the 
latter  being  the  more  so. 

(e)  Calcification. — Calcification  extends  from  the  third  to  the 
twelfth  or  thirteenth  year  of  childhood,  and  the  date  of  eruption  like 
the  maxillary  canine,  probably  precedes  the  superficial  completion  of 
its  calcification  and  occurs  about  the  eleventh  year  and  third  month. 

(/)  Pulp  Cavity  and  Root  Canals. — The  Pulp  Cavity  and  Root 
Canals  resemble  those  of  the  maxillary  teeth,  but  they  are  more 
flattened  from  side  to  side. 


THE  MANDIBULAR  SERIES  211 

(g)  Identification. — To  identify  the  tooth  it  is  necessary  to 
place  it  in  a  horizontal  position  with  the  apex  of  its  root  towards  the 
observer.  The  shorter  portion  of  the  cutting  edge  (i.  e.,  that  which 
lies  between  the  cusp  and  the  mesial  surface)  points  to  the  side 
to  which  the  tooth  belongs. 

(h)  Surgical  Anatomy.  —  In  treating  the  contents  of  the  pulp 
cavity,  an  opening  should  be  made  half-way  down  the  lingual 
surface. 

The  First  Right  Mandibular  Premolar. — The  architectural  features 
of  this  tooth  are  very  extraordinary,  exhibiting  as  far  as  its  coronal 
portion  is  concerned  gradational  changes  from  the  canine  to  the  second 
premolar.  It  is,  of  course,  a  premolar,  the  homologue  of  the  corre- 
sponding tooth  in  the  maxillary  bone,  but  it  is  not  bicuspidate,  as  it 
possesses  but  one  prominent  cusp.  The  elevation  of  the  internal 
cingulum  produces  a  small  tubercle,  which  can,  however,  in  no  sense 
be  termed  a  cusp.  It  is  an  interesting  tooth  from  a  morphological 
point  of  view. 

(a)  Mean  Measurements. — Extreme  length  from  summit  of  cusp 
to  apex,  25  mm. ;  width  across  the  greatest  diameter  (mesio-distal) 
of  the  crown,  7  mm.  Black's  figures:  Length  of  crown,  0.30;  of  root, 
0.54;  over  all,  0.84  inch. 

Variations  of  Mensuration. — The  largest  examined  was  28  mm.  long, 
and  8  mm.  wide;  and  the  smallest,   18  mm.  long,  and  8  mm.  wide. 

(&)  Crown. — There  are  five  surfaces  to  the  crown — labial,  lingual, 
mesial,  distal,  and  morsal. 

{i)  The  Labial  surfaces  resemble  in  outline  a  pentagonal  figure, 
of  which  the  base,  at  the  gingival  margin,  is  straight,  the  anterior 
border  passing  upwards  and  forwards  to  join  the  superior  mesial  border 
at  the  mesial  angle,  the  posterior,  passing  upwards  and  backwards  to 
join  the  superior  distal  border  at  the  distal  angle,  both  terminating 
at  the  extremity  of  the  cusp  in  approximately  the  central  axis  of  the 
tooth.  It  is  slightly  convex  from  before  backwards,  and  exceedingly 
so  from  above  downwards,  giving  one  the  impression  that  the  crown 
had  been  bent  inwards  towards  the  tongue.  Occasionally  it  exhibits 
horizontal  bands  of  pits.  Its  greatest  width  is  between  its  two  superior 
angles. 


212  THE  ANATOMY  OF  THE   TEETH  OF  MAN 

{ii)  Convex,  very  small  and  ill-developed  is  the  Lingual  surface. 
It  presents  mainly  a  conspicuous  tubercle  probably  formed  by  the 
elevation  of  the  cingulum. 

{Hi)  The  Mesial  surface  is  quadrangular,  its  inner  part  being  largely 
encroached  upon  by  the  very  convex  labial  surface. 

{iv)  The  Distal  is  more  concave  than  the  last  surface,  terminating 
at  the  upper  part  by  a  prominent  enlargement  of  the  mesial  angle. 

Fig.  171       Fig  172        Fig.  173       Fig.  174       Fig.  175        Fig.  176 


y.. 


^% 


Fig.  171. — The  mandibular  first  premolar — Labial  aspect.     X  -}-. 
Fig.  172. — The  same — Lingual  aspect. 
Fig.   173. — The  same — Distal  aspect. 
Fig.   174. — The  same — Mesio-distal  section. 
Fig.   175. — The  same — Labio-lingual  section. 

Fig.  176. — Various  horizontal  sections:    A,   through  the  crown;   B,  the  neck;    C, 
mid-portion;   D,  the  root;  E,  near  the  apex. 


{v)  When  viewed  from  above  the  Morsal  surface  is  roughly  tri- 
angular in  shape,  with  its  base  outwards  and  its  apex  on  the  tongue 
side.  The  prominent  cusp  occupies  nearly  the  centre  of  the  longitudinal 
axis  of  the  tooth,  and  is  the  highest  portion  of  the  crown.  From  it 
there  run  three  ridges  of  enamel:  one  anteriorly,  forming  the  upper 
mesial  border  of  the  labial  surface,  another  posteriorly,  forming  the 
upper  distal  border  of  the  labial  surface,  and  a  third  (the  median 
ridge)  running  inwards,  to  divide  the  crown  into  two  unequal  parts, 
each  of  which  is  excavated  to  form  a  deep  pit,  viz.,  the  mesial  and 
distal  pits.  Its  edges  are  all  rounded  and  well-marked.  At  times,  the 
median  ridge  is  traversed  by  a  deep  fissure  which  thus  unites  the  mesial 
and  distal  pits. 

(c)  Neck. — The  Neck  is  inconspicuous  and  lies  in  a  horizontal 
plane. 


THE  MANDIBULAR  SERIES  213 

{d)  Root. — The  Root  is,  as  a  rule,  straight,  the  labial  aspect  broader 
than  the  opposite,  and  the  mesial  than  the  distal.  The  two  former 
are  slightly  convex;  the  two  latter  slightly  concave  and  sometimes 
grooved.  This  tooth  is  often  bi-rooted,  very  rarely  triply  rooted,  the 
labial,  in  the  latter  case,  being  bifurcated.  The  apex  is  frequently 
deflected  backwards. 

{e)  Calcification. — Calcification  begins  about  the  fourth  year,  is 
superficially  completed  from  the  eleventh  to  twelfth,  and  the  tooth 
is  erupted  just  before  the  tenth. 

(/)  Pulp  Cavity  and  Root  Canals. — The  Pulp  Cavity  and  Root 
Canals  follow  the  shape  of  the  tooth.  A  cornu  may  elongate  itself 
in  the  direction  of  the  lingual  tubercle.  The  canal  is  almost  cylindrical, 
and  bifurcations  may  be  encountered  in  practice. 

(g)  Identification. — If  the  tooth  is  held  with  its  crown  upper- 
most, and  the  convex  "bent,"  labial  surface,  which  forms  such  a 
striking  feature,  nearest  the  observer  the  rounder  portion  of  the 
crown  carrying  the  mesial  pit  is  placed  on  the  side  to  which  the 
tooth  belongs. 

(/?)  Surgical  Anatomy. — Entrance  into  the  pulp  cavit}'  may  be 
effected  through  the  ridge  nearest  the  lingual  tubercle. 

The  Second  Right  Mandibular  Premolar. — It  is  often  difficult  to 
distinguish  this  from  its  homologue  in  the  maxilla.  It  is,  however, 
a  larger  tooth  with  a  quadrangular  crown,  of  which  the  upper  super- 
ficies is  smaller  than  that  at  the  neck.  This  tooth,  like  its  congener, 
possesses  one  prominent  cusp  and  several  tubercles,  the  latter  being 
raised  portions  of  the  internal  aspect  of  the  cingulum.  The  root  is 
large,  and  its  cusp  very  rounded. 

(a)  Mean  Measurements. — Extreme  length,  23  mm.;  the  labio- 
lingual  coronal  width  being  8  mm.  Black's  figures:  Length  of  crown, 
0.31 ;  of  root,  0.56;  over  all,  0.87  inch. 

Variations  of  Mensuration. — Length,  20  to  25  mm.;  width,  7.5  to 
8.5  mm. 

(&)  Coronal  Surface. — (/)  The  Labial  surface  is  larger,  and  the 
mesial  and  distal  angles  are  more  accentuated  than  the  last.  The 
extreme  apex  of  the  cusp  is  also  more  rounded;  but  it  is  not  "bent" 
inwards  so  much,  nor  is  it  so  sharply  convex. 


214 


THE  ANATOMY  OF   THE  TEETH  OF  MAN 


(ii)  The  Lingual  surface  is  well  defined.  In  shape  it  is  a  flattened 
rectangular  figure,  with  nearly  straight  sides,  its  width  being  greater 
than  its  height.  The  upper  border  betrays  a  slight  elevation  of  the 
cusps. 

{Hi)  and  {iv)  The  Mesial  and  Distal  surfaces  are  very  convex,  and 
about  equal  in  diameter  and  convexity.  Of  the  two^  the  upper  border 
of  the  former  is  the  sharper. 


Fig.  177 


Fig.  179 


Fig,  181 


Fig.  182 


Fig. 

177- 

Fig. 

178.- 

Fig. 

179. 

Fig. 

180. 

Fig. 

181. 

Fig. 

182. 

-The  mandibular  second  premolar — Buccal  aspect.     X  y- 

-The  same — Lingual  aspect. 

-The  same — Mesial  aspect. 

-The  same — Mesio-distal  section. 

-The  same — Bucco-lingual  section. 

-The  same — Various  horizontal  sections:     A,  through  the  crown;  B,  the 


neck;    C,  the  root;  D,  near  the  apex. 


(i')  The  Morsal  surface  is  quadrangular  and  possesses  four  borders — 
labial,  lingual,  mesial,  and  distal;  all  being  rounded,  and  nearly  equally' 
elevated.  A  blunt  ridge  of  enamel  extends  from  the  summit  of  the 
cusp  inwards,  a  short  distance,  and  is  traversed  by  a  deep  sulcus,  ter- 
minating in  shallow  mesial  and  distal  pits.  The  internal  border  is  well 
raised  and  very  rounded,  the  mesial  and  distal  being  less  rounded. 
The  length  of  the  fissure  between  the  pits  is  short — ra  feature  in  which 
this  tooth  simulates  its  maxillary  homologue. 

(c)  Neck. — The  Neck  lies  in  a  horizontal  plane. 

(d)  Root. — The  Root  is  very  much  longer  and  larger  than  that  of 
the  first  premolar.  Here,  as  in  that  tooth,  the  labial  aspect  is  broader 
than  the  opposite.  The  mesial  and  distal  aspects  have  similar  dimen- 
sions.    It  is,  as  a  rule,  single,  but  may  be  bifid  and  even  trifid. 

{e)  Calcification. — Calcification  begins  between  the  fourth  and 
fifth  year,   and  is  superficially  completed  between   the  eleventh  and 


THE  MANDIBULAR  SERIES  215 

twelfth.  The  tooth  erupts  before  its  completion  of  calcification, 
viz.,  at  about  ten  and  one-half  years. 

(/)  Pulp  Cavity  and  Root  Canal. — The  Pulp  Cavity  is  noted  for 
the  presence  of  two  cornua,  one  in  the  labial  and  the  other  in  the 
lingual  region,  the  latter  being  less  pronounced  than  the  former.  The 
radicular  canal  is  single,  and  much  flattened  from  side  to  side. 

{g)  Identification. — This  is  extremely  difificult.  Out  of  a  miscel- 
laneous collection  it  is  practically  impossible  to  determine,  with  cer- 
tainty, to  which  side  of  the  mandible  a  given  tooth  belongs. 

{h)  Surgical  Anatomy. — The  pulp  cavity  is  best  reached  by  drilling 
through  the  ridge  near  the  fissure  in  the  middle.  Supernumerary 
premolars  on  each  side  of  the  mandible  existed  in  a  negro,  the  cast 
of  whose  mouth  is  to  be  seen  in  the  Museum  of  the  Royal  Dental 
Hospital  of  London,  the  extra  tooth  being  placed  behind  the  other 
premolar. 

The  First  Right  Mandibular  Permanent  Molar. — This  tooth,  the 
homologue  of  the  first  maxillary  molar,  is  the  second  largest  of  all 
the  teeth.  The  sixth  from  the  midline  of  the  jaw,  it,  with  its  congener, 
shares  the  possession  of  the  greatest  number  of  arguments  regarding 
the  evolution  of  its  cusps,  and  its  importance  or  otherwise  in  ortho- 
dontics. By  most  writers  it  is  believed  to  be  the  most  frequenth- 
carious  of  all  teeth.  Thus,  Sir  John  Tomes,  from  a  series  of  extracted 
specimens,  believed  it  to  be  the  most  carious  (with  the  maxillary 
teeth)  in  42  per  cent.,  Magitot,  18  per  cent.,  and  Black,  45  per  cent. 
of  cases  as  seen  in  private  practice,  and  not  extracted  specimens.  It 
has  two  roots. 

(fl)  Mean  Measurements. — Extreme  length  from  the  apex  to  the 
external  cusp,  21  mm.;  across  the  widest  part  of  the  coronal  surface, 
12  mm.  Black's  figures:  Average  length  of  crown,  0.30;  of  root,  0.52; 
over  all,  0.82  inch. 

Variations  of  Mensuration. — The  largest  examined  measured  28 
mm.  by  13  mm.,  and  the  smallest,  17  mm.  by  7  mm.,  in  the  same 
planes. 

ijb)   Crowns. — There  are  five  surfaces  for  examination. 

(i)  Mesial:  This  is  roughly  triangular,  with  its  apex  considerably 
reduced    and    base    corresponding    with    the    neck.  _   Convex   in    both 


216 


THE  ANATOMY  OF   THE   TEETH  OF  MAN 


directions,  it  is  more  greatly  flattened  than  the  opposite  surface.  Its 
upper  border  is  furnished  with  two  acute  cusps,  which  are  part  and 
parcel  of  the  two  anterior  cusps. 

{ii)  Distally,  the  crown  partakes  very  much  of  the  same  external 
characteristics  as  the  former.  Three  acute  points  may,  however, 
be  observed  here,  the  extra  one  being  that  of  the  fifth  cusp,  which  is 
placed  on  a  somewhat  lower  level  than  the  other  two.  It  is  exceedingly 
convex  in  both  directions,  and  the  line  of  demarcation  between  its 
lower  border  and  that  of  the  root  is  practically  indistinguishable. 


Fig.  183  Fig.  184  Fig.  185  Fig.  186  Fig.  187  Fig.  i5 


n 


Fig.  183. — The  mandibular  first  molar — Buccal  aspect.     X  i- 
Fig.   184. — The  same — Lingual  aspect. 
Pig.  185. — The  same — Mesial  aspect. 
Fig.   186. — The  same — Mesio-distal  section. 
Fig.  187. — The  same — Bucco-lingual  section. 

Fig.  188. — The  same — Various   horizontal   sections:     A,   through   the   crown; 
lower  part  of  crown;  C,  the  neck;  D,  the  neck;  E,  the  roots;  F,  the  apices. 


fj  fl 


ar 


i^  F 


{Hi)  The  Buccal  surface  has  the  largest  superficies  of  any  of  the 
vertical  surfaces,  and  measures  (in  the  specimens  examined)  about 
12  mm.  as  compared  with  9  mm.  on  the  lingual  side.  It  is  convex  from 
above  downwards;  and  also  from  side  to  side,  and  again  appears,  as 
in  the  two  premolars,  as  if  it  had  been  "bent"  inwards,  the  shelving 
being  very  marked  in  some  instances.  Three  rounded  points  give  the 
upper  margin  an  almost  serrated  outline.  Unequal  in  size,  the  largest 
is  the  anterior,  the  smallest  the  posterior.  A  pit,  often,  but  by  no 
means  constantly,  is  formed  on  the  convex  surface  just  between  the 
two  anterior  points,  at  a  spot  intermediate  between  the  upper  and 
lower  borders.    The  amelo-cemental  junction  is  here  clearly  discernible. 


THE  MANDIBULAR  SERIES  217 

{iv)  The  Lingual  surface  is  quadrangular  and  its  upper  border 
exhibits  two  acute  points,  the  summits  of  the  anterior  and  posterior 
cusps.      It  is  less  convex  than  the  former. 

(lO  Roughly  trapezoidal  in  outline,  the  Morsal  surface  presents 
five  cusps  and  five  fissures  for  inspection.  The  former  occupy  the 
four  corners  of  the  figure,  and  placed  between  the  two  distal,  there  is 
a  fifth  small  cusp.  They  are  called  the  antero-external  and  internal, 
the  postero-external  and  internal,  and  the  distal  cusps.  Of  these, 
the  antero-external  is  the  largest,  the  distal  the  smallest  in  typical 
specimens.  The  antero-external  corresponds  to  the  protoconid  of  the 
primitive  triangle,  the  antero-internal  to  the  metaconid,  the  postero- 
external to  the  hypoconid,  the  postero-internal  to  the  entoconid,  and 
the  distal  to  the  hypoconulid.  There  is  no  paraconid  present  in  the 
mandibular  molars  of  Man,  according  to  Cope  and  Osborn.  The 
fissures  are  (a)  mesial  running  directly  forwards;  the  {b)  mesio-biiccal 
between  the  anterior  and  posterior  external  cusps  running  directly 
outwards;  the  (c)  disto-buccal  between  the  postero-external  and  distal 
cusps  running  backwards;  the  {d)  distal  between  the  distal  and  postero- 
internal cusps  running  backwards  and  inwards,  and  the  {e)  lingual 
between  the  two  internal  cusps  running  inwards. 

(c)  Neck. — The  Neck  is  hardly  visible,  and  lies  on  a  horizontal 
•plane.     It  is  more  or  less  quadrangular. 

{d)  Roots. — The  Roots  are  two  in  number.  The  anterior  or  mesial 
leaves  the  neck  at  first  in  a  vertical  direction,  but  soon  has  a  strong 
declension  backwards  towards  the  other  root.  It  is  the  larger  of  the 
two,  very  broad  in  the  bucco-lingual  direction.  It  has  a  slight  groove 
on  its  mesial  aspect,  and  a  deeply  excavated  groove  on  its  distal  aspect. 
Its  buccal  aspect  is  wider  than  the  other.  The  distal  root,  smaller 
than  the  last,  inclines  slightly  backwards  towards  the  socket  of  the 
second  molar.  A  groove  exists  on  its  mesial,  but  not  on  its  distal 
aspect.     Both  borders  are  of  the  same  size. 

(e)  Calcification. — Calcification  begins  during  the  eighth  month 
of  intra-uterine  life,  and  is  superficially  completed  by  the  ninth  to 
the  tenth  year.  It  erupts  midway  between  the  sixth  and  seventh  \ear 
in  30  per  cent,  of  cases. 


218  THE  ANATOMY  OF   THE   TEETH  OF  MAN 

(/)  Pulp  Cavity  and  Root  Canals. — The  Pulp  Cavity  is  roughly 
quadrilateral,  having  cornua  which  project  somewhat  into  the  four 
main  cusps.  There  are  three  root  canals,  one  in  the  distal  and  two 
in  the  mesial  root,  all  very  flattened  laterally. 

{£)  Identification. — Identification  can  be  accomplished  by  hold- 
ing the  crown  uppermost,  with  the  fifth  intermediate  cusp  away  from 
the  observer.  The  pit  on  the  buccal  surface  (if  present)  is  on  the 
opposite  side  to  which  the  tooth  belongs.  If  absent,  the  rounded 
character  of  the  same  surface  indicates  the  same  position  the  tooth 
occupies  in  the  jaw. 

Qi)  Surgical  Anatomy. — The  same  remarks  made  about  the 
opposing  tooth  in  the  upper  jaw  apply  here.  It  is  important  to 
retain  this  tooth  to  preserve  the  symmetry  of  the  dental  arches. 

The  Second  Right  Mandibular  Permanent  Molar. — This  tooth 
is  more  regular  in  outline  than  the  one  just  described.  It  is  some- 
what smaller  in  build,  rounder,  and  has  no  fifth  cusp.  Its  roots  are 
more  confluent. 

(a)  Mean  Measurements. — Extreme  length,  23  mm.  from  the 
apex  of  the  mesial  root  to  the  crest  of  the  antero-internal  cusp,  and 
II  mm.  across  the  widest  part  of  the  crown,  viz.,  the  buccal  surface. 
Black's  figures:  Average  length  of  crown,  0.27;  of  root,  0.50;  over 
all,  0.78  inch. 

Variations  of  Mensuration. — Length,  21  mm.  to  24  mm.;  width, 
10.5  to  II. 5  mm. 

ip)  Crown. — The  Crown  is  quadrilateral,  rounded,  and  symmet- 
rical. 

{i)  The  Mesial  surface  is  similar  in  every  way  to  the  corresponding 
surface  of  the  first  molar,  except  that  the  external  border  has  a  more 
curved  slope. 

(zY)  The  Distal  surface  is  like  that  of  the  first  molar,  except  that 
it  is  much  more  convex  and  rounded.  Its  junction  with  the  tooth  is 
more  highly  differentiated. 

(m)  The  Buccal  surface  resembles  the  last  named,  being  square 
in  general  outline  and  considerably  rounded.  There  is  a  tendency 
for  the  buccal  fissure  to  descend  some  short  distance  on  this  surface. 


THE  MANDIBULAR  SERIES 


219 


{iv)  The  Liu  glial  is  less  extensive  in  area  than  the  last  surface; 
its  upper  border  has  a  deep  notch  in  the  centre,  dividing  the  summits 
of  the  two  cusps.     It  is  flatter  than  the  buccal. 

{v)  The  Morsal  surface  presents  four  cusps  and  four  fissures  for 
description,  two  anterior  and  two  posterior,  named  respectively, 
from  their  situation,  antero-external  and  internal,  and  postero-external 
and  internal.  The  antero-external  cusp  represents  the  homologue 
of  the  protocol! id,  the  antero-internal  of  the  metaconid,  the  postero- 
external of  the  liypoconid,  and  the  postero-internal  of  the  entoconid. 
All  cusps  are  nearly  equal  in  size,  and  share  the  same  structural 
characteristics.  The  outer  two  have  rounded,  the  inner  two,  acute 
extremities.  The  fissures  are  deep,  and  run  straight  outwards, 
forwards,  inwards,  and  backwards. 


Pig.  189       Fig.  190      Fig.  191        Fig.  192       Fig.  193       Fig.  194 


t 


Fig.  189, 
Fig.  190 
Fig.  191 
Fig.  192 
Fig.  193 
Fig.  194, 


,a 


— The  mandibular  second  molar — Buccal  aspect.      X 

— The  same — Lingual  aspect. 

— The  same — Mesial  aspect. 

— The  same — Mesio-distal  section. 

— The  same — Bucco-lingual  section. 

— The  same — Various    horizontal    sections: 


through  the  crown;   C,  the  neck;  D,  mid-portion;  E,  the  roots;  F,  near  the  apices. 


A,    through    the    crown;    B, 


(c)   Neck. — The  Neck  lies  in  a  horizontal  plane,  and  is  well  marked. 

{d)  Roots. — Of  the  Roots,  two  in  number,  the  anterior  is  again 
the  broader  and  slightly  shorter  than  its  neighbour.  It  is  very  greath' 
deflected  backwards  and  is  rather  twisted  on  its  own  axis.  It  tapers 
gradually  to  its  apex,  is  very  flattened  from  side  to  side,  and  grooved 
on  both  aspects,  that  on  the  distal  side  being  very  pronounced.  The 
distal  root   is   straight,    narrow,    and   long.     It    too   has   a    backward 


220  THE  ANATOMY  OF  THE  TEETH  OF  MAN 

declension,  and  is  grooved  on  its  mesial  aspect.  The  distal  aspect 
is  rounded  and  slightly  concave  from  above  downwards. 

(e)  Calcification. — Calcification  begins  about  the  fifth  year  post 
natum,  and  is  superficially  completed  by  the  sixteenth  or  seventeenth 
year.     The  tooth  is  erupted  close  to  the  twelfth  year. 

(/)  Identification. — The  possession  of  a  square  crown  and  two 
roots  distinguishes  this  tooth  from  any  of  the  other  molars.  Held 
crown  uppermost,  with  the  larger  root  nearest  the  observer,  the  flat 
internal  lingual  surface  points  to  the  side  to  which  the  tooth  belongs. 

(g)  Surgical  Anatomy. — Access  to  the  pulp  cavity  can  be  best 
made  through  the  central  portion  of  the  morsal  surface. 


Fig.  195  Fig.  196  Fig.  197 


Fig.  195. — The  mandibular  third 
molar — Buccal  aspect.     X  I- 

Fig.  196. — The  same — Mesial  aspect. 

Fig.  197. — The  same — Lingual  aspect. 

Fig.  198. — The  same — Mesio-distal 
section. 


The  Third  Right  Mandibular  Permanent  Molar. — While  the  third 
molars  in  both  jaws  are  most  variable  in  shape  and  size  of  all  the  teeth, 
and  while  the  maxillary  molar  is  frequently  very  small  in  architecture, 
it  is  seldom  that  the  mandibular  third  molar  becomes  less  voluminous 
in  its  size,  but  per  contra,  it  usually  is  a  large  tooth,  and  its  variations 
tend  in  an  enlarged  direction.  It  is  frequently  entirely  suppressed. 
It  makes  its  appearance  less  irregularly  than  the  corresponding  maxil- 
lary tooth.  It  may  have  four,  or  it  may  have  five  cusps,  or  it  may  have 
seven  or  eight  diminutive  cusps. 

(a)  Mean  Measurements. — Its  greatest  diameters  may  be  i6  mm. 
and  10  mm.  in  the  coronal  region. 

Variations  of  Mensuration. — Length,  14  mm.  to  18  mm.;  width, 
8  mm.  to  12  mm. 

{b)  Crown. — The  Crown  is  difiicult  to  describe.  No  two  are  nearly 
alike.  Generally  it  may  be  averred  that  the  distal  and  buccal  surfaces 
are  the  most  convex,  the  mesial  the  flattest,  and  the  lingual  intermediate 
with   regard   to  its  convexity,   in  comparison   with  the  others.     The 


THE  MANDIBULAR  SERIES 


221 


whole   crown   has   rounded   angles  and   surfaces,    the   cusps  are  only 
slightly  elevated,  the  fissures  and  pits  on  its  morsal  surface,  shallow. 
(c)   Neck. — The  Neck  is  similar  to  that  of  the  second  molar. 


Fig.  199 


Palatal  aspect  of  right  maxilla  of  man  showing 
age  changes  of  crowns  of  the  permanent  molars,  the 
first  being  the  most,  and  the  third,  the  least 
affected.     X  jo- 

Fig.  201 


Horizontal  sections  through  the  alveolar 
process  of  the  right  half  of  the  mandible 
of  an  adult,  with  the  permanent  teeth  in 
situ.  X  ■;.  A,  at  the  gingival  margin  of 
the  bone;  B,  at  the  root  portions  of  the 
teeth.  The  shapes,  sizes,  and  positions 
of  the  pulp  cavities  and  root  canals  are 
by  no  means  constant. 


Radiograph  of  the  left  maxilla  of  a  woman,  showing 
an  impacted  mal-placed  maxillary  third  molar. 


222  THE  ANATOMY  OF  THE  TEETH  OF  MAN 

(d)  Roots. — The  Roots  are  generally  short  and  taper  rapidly  to 
their  extremities.  They  are  often  confluent.  There  may  be  two  in 
number,  the  most  normal  type — there  may  be  dichotomy  of  one  or 
two,  or  bi-dichotomy  even  may  take  place,  giving  this  tooth  four  or 
even  five  roots.    The  general  direction  of  the  roots  is  backwards. 

(e)  Calcification. — Calcification  begins  between  the  eighth  and 
ninth  years,  and  is  superficially  completed  by  the  eighteenth  year. 
It  erupts,  probably,  on  the  average  about  the  twentieth  j^ear. 

(/)  Identification. — It  is  almost  impossible  to  determine  to  which 
side  this  tooth  belongs.  If  at  all  typical,  the  description  of  the  second 
mandibular  molar  applies  also  to  this  tooth. 

(g)  Pulp  Cavity. — A  general  description  of  the  shape,  size,  and 
variations  of  this  cannot  be  given  owing  to  its  frequent  atypical  char- 
acteristics. 

(h)  Surgical  Anatomy. — This  tooth  varies  very  considerably  in 
its  position.  It  is  commonly  everted  in  an  outward  direction  and  is 
implanted  in  the  ascending  ramus  of  the  jaw.  Rarely  it  may  be  placed 
near  the  sigmoid  notch.  It  varies  in  direction,  being  frequently  tilted 
forwards.  It  may  erupt  in  a  normal  manner — or  partially — when  the 
soft  tissues  may  overlap  the  whole  or  portion  only  of  the  crown — or 
not  at  all.  It  is  often  impacted,  being  obstructed  by  the  second  molar 
through  lack  of  room  in  the  jaw.  Inflammatory  conditions  of  the 
circumdental  tissues  may  induce  tonsillitis  and  pharyngitis,  dysphagia, 
and,  if  suppurative,  trismus,  due  to  the  infiltration  of  the  inflammatory 
products.  Infection  may  spread  at  times  from  the  dental  and  maxil- 
lary veins  to  the  cavernous  sinus  through  the  pterygoid  plexus. 


THE    DECIDUOUS    TEETH 

The  architecture  copied  by  the  external  configuration  of  the  teeth 
of  the  milk  series  is  essentially  that  of  the  permanent  dentition.  The 
main  points  of  difference  lie  in  their  proportions,  each  tooth  being 
conspicuously  smaller — especially  in  the  anterior  regions  of  the  mouth — 
than  its  successor;  its  crown  is  shorter,  its  root  shorter,  and  its  neck 
more  constricted,    a  fact  very  noticeable  in   the   molar  series.     The 


THE  DECIDUOUS  TEETH  223 

latter  feature,  unless  abnormal,  enables  the  observer  to  state  at  once 
to  which  dentition  a  tooth  belongs.  The  crowns  are  more  rotund  in 
consequence.  The  deep  cervical  contraction  hitherto  believed  to  be 
occasioned  by  an  undue  prominence  and  thickening  of  the  termination 
of  the  enamel  is  caused  by  a  curious  outward  bending  of  the  dentinal 
tubes. 

In  colour  the  deciduous  are  paler  than  the  permanent  teeth. 

It  is  unnecessary  to  describe  at  all  fully  the  morphology  of  the 
Incisors,  which  follow  in  a  less  accentuated  fashion  the  conformation 
of  the  permanent  teeth.  They  are  very  conical  and  their  angles  are 
not  so  pronounced. 

At  birth,  the  straight  cutting  edge  is  trilobed,  but  the  tubercles 
quickly  disappear,  according  to  some  writers,  as  a  consequence  of 
attrition.  They  probably  afford  some  clue  to  the  mode  of  development 
of  the  enamel. 

The  roots  of  the  maxillary  teeth  are  almost  entirely  conical,  those 
of  the  lower  somewhat  flattened  on  their  mesial  and  distal  aspects. 
The  largest  of  the  four  are  the  first  maxillary  and  the  second  mandibular 
incisors.  Of  the  maxillary  teeth,  the  distal  angle  is  more  obtuse  than 
the  other,  from  an  examination  of  which  the  side  of  the  mouth  to 
which  it  belongs  can  be  readily  ascertained. 

Of  the  incisors  it  is  difficult  to  differentiate  between  the  first  and 
second,  as  in  both  instances  the  angles  are  more  or  less  acute. 

The  crowns  of  the  Canines  are  usually  somewhat  conical  in  shape, 
having  surfaces  as  in  the  corresponding  permanent  teeth.  Of  these, 
that  on  the  labial  side  presents  a  slight  prominence  in  a  vertical 
direction. 

The  neck  occupies  a  plane  which  is  more  horizontal  than  in  the 
incisor.  It  is  also  more  pronounced.  It  is  difficult  to  discriminate 
between  those  implanted  in  the  upper  and  in  the  lower  jaw,  but  of 
the  two  it  is  probable  that  the  latter  is  slightly  the  smaller.  The 
distal  angle  is  very  rounded. 

The  Molars  correspond  closely'  to  the  patterns  of  the  permanent 
teeth.  The  crowns,  however,  are,  on  the  whole,  shorter.  They  are 
very  disproportionate  in  size,  the  second  being  much  larger  than  the 
first.     Each  crown  has  five  surfaces:  a  morsal,  buccal,  lingual,  mesial, 


224 


THE  ANATOMY  OF  THE  TEETH  OF  MAN 


and  distal.     The  former  has  three,  four,  or  five  cusps,  separated  by 
sulci  of  varying  depth.     The  cusps  differ  in  height;  in  the  maxilla,  those 


Fig.  202        Fig.  203        Fig.  204      Fig.  205 


Fig.  202. — The  maxillary  deciduous  first  incisor 
— Labial  aspect.     X  ij- 

Fig.  203. — The  mandibular  deciduous  first  incisor 
— Labial  aspect.     X  to- 

Fig.  204. — The  maxillary   deciduous   second  in- 
cisor— Labial  aspect.     X  tit- 
Fig.  205. — The  mandibular  deciduous  second  in- 
cisor— Labial  aspect.     X  jo- 


? 


Fig.  206      Fig.  207      Fig.  208      Fig.  209      Fig.  210 


Fig.  206. — The  maxillary  deciduous 
canine — Labial  aspect.      X  j . 

Fig.  207. — The  same — Lingual  aspect. 

Fig.  208. — The  same — Distal  aspect. 

Fig.  209. — The  same  —  Labio-lingual 
section. 

Fig.  210. — The  same  —  Mesio-distal 
section. 


Fig.  211. — The  mandibular  deciduous 
canine — Labial  aspect.     X  i- 

Fig.  212. — The  same — Lingual  aspect. 

Fig.  213. — The  sam.e  —  Mesio-labial 
aspect. 

Fig.  214. — The  same  —  Labio-lingual 
section. 

Fig.  215. — The  same  —  Mesio-distal 
section. 


Fig.  211       Fig.  2J2      Fig.  213      Fig.  214      Fig.  215 


! 


Fig.  216 


Fig.  217 


Fig.  219 


Fig.  220 


Fig.  216. — The  maxillary 
deciduous  first  molar — 
Distal  aspect.      X  t- 

Fig.  217. — The  same — 
Mesial  aspect. 

Fig.  218. — The  same — 
Buccal  aspect. 

Fig.  219. — The  same — 
Bucco-lingual  section. 

Fig.  220. — The  same — 
Mesio-distal  section. 


on  the  lingual  side  are  more  elevated  than  the  others;  in  the  mandible 
the  opposite  rule  obtains.     The  roots,  three  in  number,  of  the  upper 


THE  DECIDUOUS   TEETH 


series  are  cylindrical,   widely  divergent  in  the  first,   and  less 
second. 

Fig.  221  Fig.  222        Fig.  223       Fig.  224 

Fig.  221. — The  mandibular  decid  ■ 
uous  first  molar — Buccal  aspect.   X  j. 

Fig.  222. — The  same  —  Lingual 
aspect. 

Pig.  223. — The  same  —  Distal 
aspect. 

Fig.  224. — -The  same  —  Mesio- 
distal  section. 

Fig.  225. — The  same  —  Bucco- 
lingual  section. 


in   the 

Fig.  225 


t 


Fig. 


Fig.  228 


Fig.  229 


*f 


Fig.  230 


Fig.  226. — The  maxil- 
lary deciduous  second 
molar — Mesial  aspect.  X}. 

Fig.  227. — The  same — 
Distal  aspect. 

Fig.  228. — The  same — 
Buccal  aspect. 

Fig.  229. — The  same — 
Mesio-distal  section. 

Fig.  230. — The  same — 
Bucco-lingual  section. 


Fig.  231.  —  The  man- 
dibular deciduous  second 
molar  —  Lingual  aspect. 
X  }. 

Fig.  232. — The  same — ■ 
Buccal  aspect. 

Fig.  233. — The  same — 
Distal  aspect. 

Fig.  234. — The  same — 
Mesio-distal  section. 

Fig.  235. — The  same — 
Bucco-lingual  section. 


W  il  •  ^  N 


Fig.  231 


Fig.  232 


Fig.  233 


Fig.  234 


Fig.  235 


The  first  maxillary  molars  are  somewhat  triangular  in  outline,  the 
lower  more  flattened  on  their  labio-lingual  surfaces.  The  former  has 
three  cusps:  one  on  the  lingual  side,  two  on  the  buccal.  Occasionally 
this  tooth  has  the  appearance  of  a  small  premolar.  Of  the  four  cusps 
of  the  second  molar,  the  postero-external  is  joined  to  the  antero-internal 
by  an  oblique  ridge,  which,  therefore,  runs  outwards  and  slightly  back- 
wards. 
15 


226  THE  ANATOMY  OF  THE  TEETH  OF  MAN 

The  lower  second  molar  possesses  five  cusps,  three  placed  externally 
(the  most  posterior  being  the  smallest),  and  two  on  the  lingual  side. 
The  position  of  the  fifth  cusp  is  a  guide  to  the  identification  of  the 
tooth. 

Size. — The  Variations  in  the  size  of  the  deciduous  teeth  are  very 
small.  Just  as  there  is,  as  a  rule,  but  little  deviation  from  their  posi- 
tion in  the  dental  arch,  so  the  measurements  of  the  teeth  are  fairly 
constant,  much  more  so  than  their  successors.  If  large,  they  are 
collectively  so,  not  isolated  or  symmetrical,  as  for  instance,  in  the 
first  permanent  incisors. 

The  following  figures  represent  the  average  widths  of  the  crowns 
of  these  teeth,  on  their  labial  surfaces,   taken  in  millimetres:" 

e         d         c         b         a  abode 

8-6     68     66     5-3     62   I  65     52     6'6     6-8     85 
9'4     7'8     5'7     4'4    3'8  |  3'8     4'4     5'6     77     9'6 

Variations  of  Mensuration. — First  Incisors — 5.6  to  7.0;  Second 
Incisors — 4.2  to  6.0;  Canines — 5.7  to  7.1;  First  Molars — 6.0  to  7.5; 
Second  Molars — 6.7  to  9.0  mm. 

Surgical  Anatomy. — Caries  of  these  teeth  leading  to  inflammation 
of  the  pulp  and  its  subsequent  suppuration  often  leaves  its  mark 
behind  in  structural  changes  of  the  enamel  of  the  permanent  teeth, 
such  as  hypoplasia,  and  perhaps  a  certain  amount  of  discolouration. 


AGE    CHANGES    IN    THE    TEETH 

In  colour,  the  blue  whiteness  of  young  specimens  disappears  and 
gives  place  to  a  yellow  tinge  attrition,  the  middle  portions  of  the  cutting 
edges  of  the  incisors  often  become  discoloured  and  brown,  and  remind 
one  somewhat  of  the  "marks"  in  the  teeth  of  the  horse.  This  is  best 
observed  in  the  molars,  when  the  cusps  have  been  worn  away  and  a 
table  of  varying  pattern  remains. 

The  roots  become,  as  age  advances,  translucent,  especially  those  of 
the  mandibular  incisors.  Exactly  how  this  is  produced  is  not  yet 
known;  it  is  believed  to  be  due  to  a  calcification  of  the  hard  tissues, 
which  causes  a  closing  of  the  dentinal  tubes  and  an  approximation  of 


AGE  CHAXGES  IN   THE   TEETH  227 

the  refractive  indices  of  the  matrix  and  the  tubules.  It  is  important 
to  note  that  old  age  changes  in  the  dentine,  cementum,  pulp,  or  perio- 
dontal membrane  are  quite  independent  of  the  age  of  the  patient. 
The  teeth  of  children  frequently  exhibit  senile  conditions,  the  crowns 
often  becoming  faceted,  and  the  pulps  undergoing  fibroid  degeneration. 

References 

1.  Amoedo.    "Les  Dents,  "  Traite  d' Anatomic  Humaine,  par  P.  Poirier  et  A.  Charpy,  1900 

2.  Barden.    "Nomenclature  anglo-americaine  ou  Nomenclature  rationelle, "  Revtie  odontologique, 
1911. 

3.  Black.     "A  Work  on  Operative  Dentistry,"  1908,  vol.  i. 

4.  Black.    "Descriptive  Anatomy  of  the  Human  Teeth, "  1894. 

5.  Broomell.    "The  Anatomy  and  Histology  of  the  Mouth  and  Teeth,  "  1892. 

6.  Burchard  and  Inglis.    "A  Text-book  of  Dental  Pathology  and  Therapeutics,  "  1912. 

7.  Choquet.    "Precis  d'Anatomie  Dentaire,  "  1903. 

8.  Constant.    "The  Naked-ej'e  Anatomy  of  the  Human  Teeth,"  1905. 

9.  Dieulafe  et  Herpin.    "Anatomic  de  la  Bouche  et  des  Dents, "  1909. 

10.  Dolamore.     "The  Relation  of  the  Deciduous  to  the  Permanent  Dentition,"  Royal  Dental 
Hospital   Gazette,    1908. 

11.  Fischer.    "Bau  und  Entwickelung  der  Mundhohle  des  Menschen,  "  1909. 

12.  James  and  Pitts.    "Some  Notes  on  the  Dates  of  Eruption  in  Four  Thousand  Eight  Hundred 
and  Fifty  Children,  Aged  under  Twelve, "  Proc.  Roy.  Soc.  of  Med.,  1912. 

13.  Magitot.    "Recherches  sur  la  Carle  des  Dente, "  1871. 

14.  Redier.    "Precis  de  Stomatologic, "  1909. 

15.  Tomes,  Sir  John.    "Lectures  on  Dental  Physiology  and  Surgery,"  1848. 
i6.  Tomes  and  Nowell.    "A  System  of  Dental  Surgery, "  1906. 

17.  Tomes,  Charles  S.    "A  Manual  of  Dental  Anatomy,"  1908. 


CHAPTER    XI 
THE   RELATIONSHIPS   OF  THE   TEETH   OF   MAN 

The  Mutual  Association  of  the  Teeth  with  the  Mouth  and  Osseous  System. — The  Nervous  System. 
— The  Vascular  System. — The  Lymphatic  System. 

The  importance  of  and  clinical  significance  attaching  to  the  subject 
about  to  be  discussed  is  probably  second  to  no  other  which  has  been 
occupying  the  attention   of  the  reader.      Too  frequently   the  dental 


Fig 


The  surface  markings  of  the  superficial  structures  of  the  face  and  neck.  The  positions  of  the 
parotid  gland  and  Stenson's  duct  are  shown  in  white  outline;  the  points  o'f  emergence  of  the  supra- 
orbital, infra-orbital,  and  mental  nerves  in  white,  with  black  centres;  and,  in  black,  the  six  branches 
of  the  terminations  of  the  facial  nerve,  the  facial  artery,  and  the  superficial  temporal  artery  dividing 
into  anterior  and  posterior  branches.  The  outlines  of  the  sternocleidomastoid  muscle,  the  sub- 
maxillary triangle,  the  superior  carotid  triangle,  the  inferior  carotid  triangle,  and  the  subclavian 
triangle  are  also  indicated.    The  condyle  can  be  felt  immediately  in  front  of  the  tragus. 


PLATE   II 


■<fN» 


i 


A  Human  Skull  in   Norma  Lateralis.    X  t% 


THE  MOUTH  AND  OSSEOUS  SYSTEM 


229 


surgeon  forgets  that  the  teeth  are  part  and  parcel  of  the  human  economy 
and  treats  them  as  if  they  were  something  separate.  Here,  however, 
their  relationships  to  the  associated  parts  will  be  narrated  in  order 
to  draw  attention  to  their  close  connexion  with  other  systems  of  the 
body  and  the  bearing  this  topography  has  upon  them. 

It  will  be  convenient  to  describe  these  observations  under  the  sub- 
divisions of: 

A.  The  Mouth  and  Osseous  System  and  the  Dental  Arches. 

B.  The  Nervous  System — 

(i)  Anatomical. 
{ii)   Physiological. 

C.  The  Vascular  System. 

D.  The  Lymphatic  System. 

THE    MOUTH    AND    OSSEOUS    SYSTEM 


The  oral  cavity  has  in  front  a  transverse  aperture,  the  rima  oris; 
behind,  it  communicates  with  the  pharynx  through  the  isthmus  faucium. 

Fig,  237 


Diagram  of  coronal  section  of  the  mouth  behind  the  second  molar  tooth.  X  A-  (After  Johnson 
Symington.)  VO,  vestibidum  oris;  CO,  cavum  oris;  SALS,  superior  alveolo-labial  sulcus;  lALS, 
inferior  alveolo-labial  sulcus;  Max,  maxilla;  Man,  mandible;  T,  tongue. 

The  cavity  is  divided  into  two  parts:  An  outer  [vestihuhim  oris), 
bounded  externally  by  the  lips  and  cheeks,  and  internally  by  the  teeth 
and  gums  which  cover  the  outer  aspect  of  the  alveolar  process  of  the 
jaws.     The  roof  and  floor  are  formed  by  a  reflexion  of  the  mucous 


230  THE  RELATIONSHIPS  OF   THE   TEETH  OF  MAN 

membrane  of  the  lip^  and  cheeks  inwards  to  the  alveolar  processes, 
which  it  joins  about  the  level  of  the  middle  of  the  roots  of  the  teeth. 
The  extension  upwards  and  downwards  of  the  vestibule  of  the  mouth 
forms  the  superior  and  inferior  alveolo-labial  or  buccal  sulci.  A  vertical 
fold  of  mucous  membrane  is  found  in  the  middle  line  called  the  frcenum 
lata. 

With  the  mouth  closed,  the  following  soft  parts  externally  covering 
the  teeth  are  observed : 

The  buccal  orifice,  separating  the  upper  and  lower  lips,  having  at 
each  extremity  the  buccal  commissure,  the  naso-labial  furrow,  inter- 
vening in  the  middle  line  between  the  upper  lip  and  the  base  of  the 
nose,  and  beneath  the  lower  lip  in  the  midline,  the  labio-mental 
depression. 

Inspection  of  the  mouth  considerably  open  shows  in  the  midline 
the  frcenum  labii  superioris  et  inferioris,  the  dental  arches  and  gums, 
the  pale  mucous  membrane  of  the  hard  and  soft  palates,  the  isthmus 
of  the  fauces,  the  uvula,  the  anterior  pillar  of  the  fauces,  and  occasion- 
ally the  tonsils.  Occupying  the  floor  of  the  mouth  is  the  dorsum  of 
the  tongue,  which  if  raised,  exhibits  on  its  inferior  surface  in  the 
midline  the  lingual  fraenum,  the  sublingual  folds,  with  the  sublingual 
caruncle  (the  orifice  of  the  sublingual  duct)  in  close  proximity  to  the 
frcenum  linguce  and  higher  up  the  ranine  folds  (Fig.  239),  and  an  inner- 
most portion  called  the  cavum  oris,  which  lies  inside  the  concavities 
formed  by  the  dental  arches.  The  roof  is  the  hard  and  soft  palate; 
the  floor,   the  tongue. 

The  Parotid  Salivary  Gland  opens  into  the  former  by  means  of  the 
parotid  duct  opposite  the  buccal  aspect  of  the  crown  of  the  second 
maxillary  molar,  and  the  submaxillary  and  sublingual  glands  open 
into  the  latter.  Of  these  the  duct  of  the  submaxillary  salivary  gland 
(Wharton's)  terminates  by  a  narrow  orifice  on  the  summit  of  the  sub- 
lingual caruncle,  at  the  side  of  the  frcenum  linguce;  and  the  ducts  of 
the  sublingual  salivary  gland,  of  which  there  may  be  ten  to  twenty, 
end,  some  by  uniting  to  form  a  tube  (the  duct  of  Bartholin)  to  open 
into  the  Whartonian  duct,  the  others  (the  ducts  of  Rivini)  to  open 
separately  into  the  mouth  through  small  apertures  in  the  mucous 
membi'ane  lying  over  the  gland  itself. 


THE  MOUTH  AND  OSSEOUS  SYSTEM 


231 


During  the  occlusion  of  the  teeth,  the  vestibulum  oris  and  cavum 
oris  communicate  only  through  the  interdental  spaces,  and  a  larger 
opening  placed  behind  the  third  molar  and  in  front  of  the  ramus  of 
the  jaw  (Fig.  237). 

The  labial  mucous  glands  open  on  the  inner  aspect  of  the  lips,  being 
situated  between  the  mucous  membrane  and  the  orbicularis  oris  muscle. 
The  buccal  glands  lie  between  the  mucous  membrane  of  the  cheek 
and  the  buccinator  muscle.  The  molar  glands  are  found  between  the 
masseter  and  buccinator  muscles;  they  are  larger  than  the  others, 
and  the  terminations  of  their  short  separate  ducts  are  placed  in  the 
immediate  neighbourhood  of  the  third  molar. 

Fig.  238 


A  B 

Diagram  of  the  buccal  cavity,  A,  with  the  tongue  on  the  floor  of  the  mouth;  and  B,  raised  to  show 
its  under  surface.  U.F.,  frenum  of  upper  hp;  L.F.,  frenum  of  lower  lip;  P.,  vault  of  the  palate; 
J.,  junction  of  the  hard  and  soft  palates  in  the  middle  line;  V.,  uvula;  P.P. A.,  posterior  palatine 
artery;  I.F.,  isthmus  of  the  fauces;  P.P. P.,  posterior  pillar  of  the  fauces;  A. P. P.,  anterior  pillar 
of  the  fauces;  P.,  tongue;  L.N.,  lingual  nerve;  R.A.,  ranine  artery;  F.L.,  frsnum  linguae;  S.C., 
sublingual  caruncle  (orifice  of  Wharton's  duct). 


The  palate  consists  of  the  hard  and  soft  palates.  In  sagittal  section 
it  is  concave  from  before  backwards  and  also  from  side  to  side.  There 
exist  many  variations  in  its  shape  and  size.  Broca  described  four  main 
forms  depending  on  the  direction  of  its  walls.  Dieulafe  and  Tournier- 
take  note  not  only  of  this  anatomical  factor,  but  also  of  the  curve  of 


232  THE  RELATIONSHIPS  OF   THE  TEETH  OF  MAN 

its  summit.  In  70  per  cent,  of  cases  the  type  presented  an  arch  with 
a  rounded  summit  and  convergent  walls,  which  they  designated  the 
(i)  elliptical  form;  (/i)  in  22  per  cent,  of  cases  there  were  convergent 
walls  with  a  flattened  roof;  {in)  in  6  per  cent,  a  rectilinear  summit 
with  slightly  divergent  walls,  and  {iv)  in  4  per  cent.,  "un  type  arrondi 
et  a  branches  divergentes,  hyperbolique"  (Fig.  239). 

Fig.  239 


Diagram  showing  the  four  main  types  of  shapes  of  the  arch  of  the  palate  in  man.  (After  Dieulafe 
and  Tournier.)  A,  the  elliptical  (70  per  cent.);  B,  the  semi-elliptical  (20  per  cent.);  C,  the  divergent 
(5  per  cent.);  D,  the  hyperbolic  (4  per  cent.). 

The  palatal  rugae,  which  are  merely  thick  mucosa,  are  arranged 
longitudinally  and  transversely.  In  the  middle  line  there  is  a  longi- 
tudinal ridge  or  raphe  which  ends  between  the  two  first  incisors  in  an 
eminence,  the  incisive  pad,  "alveolar  point,"  or  papilla  palatina.  The 
papilla  corresponds  with  the  anterior  palatine  fossa,  and  receives 
the  terminations  of  the  naso-palatine  and  anterior  palatine  nerves. 
On  its  surface  there  are  sometimes  found  two  small  cuts  de  sac  which 
represent  the  orifices  of  the  foramen  of  Stenson. 

Stenson's  duct,  two  and  a  half  inches  in  length,  opens  opposite  the 
crown  of  the  second  maxillary  molar,  and  Wharton's  duct,  two  inches 
long,  close  to  the  side  of  the  frceniim  linguce. 

The  antrum  of  Highmore  is  a  cavity  in  the  superior  maxilla  which 
varies  very  considerably  in  shape,  size,  and  cubic  capacity.  Roughly 
triangular,  its  apex  is  placed  towards  the  malar  process  of  the  bone, 
its  base  to  the  outer  wall  of  the  nose,  its  walls  corresponding  to  the 


THE  MOUTH  AND  OSSEOUS  SYSTEM  233 

orbital,  facial,  and  zygomatic  surfaces  of  the  superior  maxilla.  Cross- 
ing its  posterior  wall  are  the  posterior  dental  canals. 

The  roots  of  the  first,  second,  and  third  maxillary  molars  very 
frequently'  project  slightly  into  it,  but  at  times  there  may  be  direct 
communication  between  the  sockets  of  both  premolars,  and  even  the 
canine. 

The  Dental  Arches. — Of  these  the  upper  is  elliptical,  the  lower, 
parabolic  in  outline.  The  former  is  rather  longer  than  the  latter,  so 
that  the  maxillary  teeth  slightly  overlap  those  of  the  mandible  in  front 
and  at  the  sides.  There  may  be  several  deviations  from  this  rule, 
as  explained  and  described  by  Choquet.^ 

There  is  no  diastema  in  the  jaws  of  Man.  But  Professor  Duckworth 
(see  Chapter  IX)  considers  it  not  very  rare  in  European  skulls,  and 
fairly  common  in  the  natives  of  New  Guinea. 

The  Mutual  Relationships  of  the  Permanent  Teeth. — The  teeth 
in  Man  do  not,  in  normal  circumstances,  occlude  by  means  of  their 
cusps,  but  by  a  perfect  system  of  interdigitation.  Indeed,  Nature 
has  made  the  shapes  of  human  molar  teeth  so  perfectly,  that  they 
cannot  do  harm  to  the  soft  muscular  tissues  with  which  they  come  into 
contact,  and  by  means  of  their  rounded  and  bunodont  character  are 
efficient  masticators;  and  while  they  lose  their  protective  cuticle 
(Nasmyth's  membrane),  by  abrasion,  over  the  summits  of  these 
cusps,  provides,  here,  self-cleansing  surfaces  with  regard  to  the  eating 
of  food. 

The  morsal  surfaces  of  the  premolars  and  molars  are  not  in  the  same 
horizontal  plane,  that  of  the  lower  cheek  teeth  forming  a  slight  curve 
the  concavity  of  which  receives  the  morsal  surfaces  of  the  upper  teeth 
arranged  in  a  gentle  convexity,  the  curve  of  Graf  von  Spee.  The 
cutting  edges  of  the  mandibular  incisors  and  canines  form  a  rather 
less  marked  curve,  the  convexity  of  which  looks  upwards. 

There  is  coincidence  of  the  central  lines  of  the  two  arches.  In  occlu- 
sion— vulgarly  termed  articulation — the  maxillar}^  first  incisors  over- 
lap the  upper  third  of  the  labial  surfaces  of  the  two  corresponding" 
mandibular  teeth.  They  also,  from  the  disparity  in  the  size  of  the 
lower  teeth,  overlap  the  whole  of  the  crown  of  the  first  and  about  half 
of  the  second  incisor  in  a  lateral   direction. 


234  THE  RELATIONSHIPS  OF  THE  TEETH  OF  MAN 

The  lingual  aspect  of  the  maxillary  second  incisor  overlaps  the 
labial  surface  of  the  lower  corresponding  tooth  and  the  canine;  the 
lingual  surface,  therefore,  of  the  upper  first  incisor  occludes  with  the 
upper  part  of  the  labial  surfaces  of  the  two  lower  incisors,  and  the 
lingual  surface  of  the  upper  second  incisor  with  the  labial  surfaces 
of  the  mandibular  second  incisor  and  canine. 

The  labial  surface  of  the  mandibular  canine  strikes  against  the 
lingual  surface  of  the  maxillary  canine,  which  occludes  also  on  its 
distal  portion  with  the  buccal  surface  of  the  first  mandibular  pre- 
molar. 

Fig.  240 


Occlusion  of  the  permanent  teeth  of  an  adult  man 


Other  occlusions  of  the  cheek  teeth  must  be  briefly  described,  and 
are  as  follows: 

(A)  The  distal  portion  of  the  large  external  cusp  of  the  first  man- 
dibular premolar,  with  the  mesial  ridges  of  the  buccal  and  lingual 
cusps  of  the  upper  corresponding  teeth. 

(B)  Both  external  and  internal  cusps  of  the  first  maxillary  pre- 
molar in  front,  and  the  mesial  ridges  of  the  same  cusps  of  the  second 
premolar  behind,  with  the  buccal  cusp  of  the  second  mandibular 
premolar. 


THE  MOUTH  AND  OSSEOUS  SYSTEM  235 

(C)  The  internal  cusp  of  the  maxillary  first  premolar  with  the 
distal  ridges  of  both  cusps  of  the  lower  first  premolar  in  front,  and 
the  mesial  ridges  of  both  cusps  of  the  second  mandibular  premolar 
behind. 

(D)  The  internal  cusp  of  the  second  maxillary  premolar  inter- 
digitates  with  the  posterior  ridges  of  the  two  cusps  of  the  second 
mandibular  premolar  in  front,  and  behind  with  the  antero-external 
and  antero-internal  cusps  of  the  first  molar. 

(E)  The  antero-external  cusp  of  the  first  mandibular  molar  occludes 
with  the  distal  ridges  of  both  cusps  of  the  second  maxillary  premolar 
in  front,  and  the  antero-external  and  antero-internal  cusps  of  the 
maxillary  first  molar  behind,  while  the  antero-external  cusp  of  the 
lower  first  molar  occludes  with  the  central  portion  of  the  morsal  sur- 
face of  the  upper  first  molar,  and  the  postero-external  with  the  posterior 
portion  of  the  morsal  surface  of  the  same  tooth. 

(F)  The  antero-external  cusp  of  the  first  maxillary  molar  interdigi- 
tates  with  the  central  sulcus  of  the  corresponding  lower  tooth,  in  front, 
and  the  postero-external  with  the  postero-lingual  and  postero-buccal 
cusps  of  the  first  mandibular  molar  and  the  antero-external  and 
antero-internal  of  the  second  lower  molar. 

(G)  The  antero-external  cusp  of  the  second  mandibular  molar 
meets  the  postero-external  and  postero-internal  cusps  of  the  first  maxil- 
lary molar  in  front,  and  the  antero-external  and  antero-internal  cusps 
of  the  second  maxillary  molar  behind.  The  postero-internal  cusp  of 
the  second  lower  molar  coincides  with  the  central  part  of  the  crown 
of  the  second  upper  molar. 

(H)  The  antero-external  cusp  of  the  second  maxillary  molar  occludes 
with  the  central  part  of  the  crown  of  the  second  mandibular  molar, 
and  the  postero-external  cusp,  with  both  posterior  cusps  of  the  second 
mandibular  molar  in  front,  and  both  the  anterior  cusps  of  the  third 
mandibular  molar  behind. 

Variations. — These  conditions  obtain  in  normal  occlusion  of  the  teeth. 
It  is  very  obvious,  however,  that  many  variations  maj'  and  do  occur. 
Orthodontics  is  a  branch  of  dental  surgery  based  upon  these  irregu- 
larities and  deviations  from  the  normal  and  orthodontical  science  and 
art  aims  at  their  study  and  correction.     Clinically,  some  of  them  are 


236 


THE  RELATIONSHIPS  OF  THE   TEETH  OF  MAN 


spoken  of  as  "edge  to  edge  bite,"  "superior  protrusion,"  "open  bite," 
"underhung  bite,"  etc.,  clumsy  definitions  which  are  more  forcible 
than  accurate  (see  Preface). 


Fig.  241 


Radiograph  of  the  normal  jaws  of  an  adult,  aged  nineteen  years.     There  were  no  evidences  of 
dental  or  oral  disease,  and  there  was  no  caries.     Cf.  Fig.  294. 


THE  MOUTH  AND  OSSEOUS  SYSTEM 
Fig.  242 


237 


Human  skull  showing  enharmosis.     X 
Fig.  243 


The  same — fromt  aspect. 


238 


THE  RELATIONSHIPS  OF  THE  TEETH  OF  MAN 


With  a  view  of  placing  these  atypical  modifications  on  a  scientific 
basis,  Grevers,^  of  Utrecht,  following  up  the  work  of  Iszlay,  Stenfeld, 
and  L.  Meyer,  suggests  certain  terms  to  signify  these  anomalies. 

Fig.  244 


Human  skull  showing  prosharniosis.      X 
Fig.  245 


The  same — front  aspect. 


THE  MOUTH  AND  OSSEOUS  SYSTEM 

Fig.  246 


239 


Human  skull  showing  di-enharmosis.     X 
Fig.  247 


The  same — liont  aspect. 


240 


THE  RELATIONSHIPS  OF   THE  TEETH  OF  MAN 


Thus  the  normal  position  of  the  teeth  in  the  dental  arches  and  in 
contact  with  one  another,  as  already  described,  is  known  as  enharmosis. 


Fig.  248 


H^HilfV' 


Human  skull  showing  epharmosis.     X  |. 

He  proposes  the  use  of  such  terms  as 
I.    Eitharmosis — a  normal  bite,  maxillary  teeth  projecting  slightly. 
II.    Epharmosis — an  "underhung  bite,"  mandibular  teeth  project- 
ing. 

III.  Prosharmosis — an  "edge  to  edge"  bite. 

IV.  Opharmosis — an  "open  bite." 

V.    Disharmosis — a  "cross  bite,"  so-called. 

VI.    Tyrpharmosis — a  mixed  up,  irregular  bite  which  does  not  come 

under  any  of  the  preceding  headings,  and  may  be  a  mixture 

of  two  or  more. 

Each  of  these  groups  can  be  further  differentiated  from  the  others. 

Thus  if  the  occlusion  is  quite  typical,  the  condition  is  called  eu-enhar- 

mosis;  if  the  space  between  the  upper  and  lower  teeth  is  greater — • 

di -enharmosis;  and  if  the  upper  teeth  cover  the  labial  surfaces  of  the 


THE  NERVOUS  SYSTEM  241 

lower  entirely,  and  the  latter  actually  bite  in  the  mucous  membrane 
of  the  hard  palate,  the  condition  may  be  called  dys-enharmosis. 

In  Group  11  a  reversed  state  may  be  sometimes  noticed,  and  using 
the  three  affixes  already  noted,  spoken  of  as  eu-epharmosis,  when  the 
lower  teeth  touch  the  labial  surfaces  of  the  upper  and  no  intervening- 
space  exists;  di-ephannosis  the  same,  but  when  a  great  space  exists; 
and  dys-epharmosis  when  the  lower  series  cover  the  upper  teeth  entirely 
with  little  space  intervening. 

The  other  groups  may  be  similarly  subdivided.  By  noting  these 
terms  the  writer  would  urge  the  reader  to  adopt  this  newer  and  more 
scientific  nomenclature. 


THE    NERVOUS    SYSTEM 

This  probably  is  the  most  important  from  a  physiological  and 
clinical  and  pathological  point  of  view. 

Anatomical  Relationships. — The  anatomical  relationships  may  be 
now  briefly  described. 

Upper  Jaw. — In  the  upper  jaw,  the  superior  maxillary,  or  the  second 
division  of  the  fifth  pair  of  nerves,  gives  oflf,  in  the  spheno-maxUlary 
fossa, 

(i)  The  Posterior  Superior  Dental  Branches. — These  arise  from  the 
trunk  as  it  is  about  to  enter  the  infra-orbital  canal.  Two  in  number, 
they  immediately  bifurcate,  and  pass  downwards  towards  the  maxillary 
tuberosity.  They  supply  the  gums  and  neighbouring  mucous  mem- 
branes of  the  cheek.  Traversing  the  posterior  dental  canals  on  the 
zygomatic  surface  of  the  maxilla,  and  passing  from  behind  forwards 
to  the  body  of  the  bone,  they  then   communicate  with  the 

(//)  Middle  Superior  Dental  Nerve,  give  off  branches  to  the  antral 
mucosa,  and  pass  into  the  pulps  of  each  of  the  three  nwlars. 

The  pulps  of  the  premolars  are  supplied  by  the  terminations  of  the 
middle  superior  dental  branch  which  is  given  off  in  the  back  portion 
of  the  infra-orbital  canal,  and  runs  downwards  and  forwards  in  a  special 
canal  in  the  outer  wall  of  the  antrum.  It  communicates  with  the 
posterior  and  anterior  dental  branches,  through  the  so-called  Ganglion 


242  THE  RELATIONSHIPS  OF   THE  TEETH  OF  MAN 

of  Valentin  with  the  former,  and  the  so-called  Ganglion  of  Bochdalek 
with  the  latter. 

{iii)  The  Anterior  Superior  Dental  Branch,  of  large  size,  comes 
off  from~the  superior  maxillary  nerve  just  before  it  emerges  from  the 
infra-orbital  foramen.  It  runs  in  a  special  canal  in  the  anterior  wall 
of  the  antrum,  passes  from  before  backwards  and  divides  into  a  series 
of  branches  to  supply  the  pulps  of  the  canines  and  incisors.  It  commu- 
nicates with  the  middle  dental  branch  and  gives  off  a  small  nasal 
branch,  which  inosculates  with  the  naso-palatine  nerve  from  Meckel's 
ganglion. 

Lower  Jaw. — In  the  lower  jaw:  The  inferior  dental  (mandibular) 
nerve  is  the  largest  of  the  three  branches  of  the  inferior  maxillary 
nerve.  It  passes  with  the  inferior  dental  artery  beneath  the  external 
pterygoid  muscle,  and  then  between  the  internal  lateral  ramus  of  the 
jaw  to  the  dental  foramen.  Running  forwards  in  the  dental  canal 
and  lying  beneath  the  teeth,  as  far  as  the  mental  foramen,  it  there 
divides  into  incisive  and  mental  branches.  The  incisors  and  canines 
are  supplied  by  the  incisive  branch,  the  premolars  and  molars  by  the 
dental  branches.     (See  the  Frontispiece.) 

The  mental  branch  freely  inosculates  with  the  facial  nerve. 

Physiological  Relationships. — The  nervous  system  of  the  masticat- 
ing organs  when  viewed  from  a  physiological  and  a  clinical  aspect  is 
of  the  utmost  importance  and  should  be  of  great  assistance  in  the 
diagnosing  of  difficult  recondite  problems  of  pain  in  dental  surgery. 
A  knowledge  of  the  topography  of  the  clinical  areas  of  Dr.  Henry 
Head*  is,  on  occasion,  of  the  highest  value.  This  learned  investigator 
has  established  a  definite  relationship  between  certain  visceral  dis- 
turbances in  head,  thorax,  and  abdomen,  with  well-marked  areas  of 
superficial  tenderness  on  the  skin  in  the  neighbourhood.  In  an  elaborate 
paper,  he  successfully  shows  that  "each  organ  of  the  head  (including 
teeth)  stands  in  relation  with  one  or  more  areas  on  the  surface.  To 
these  areas,  pain  is  referred,  and  over  them  the  skin  may  become  tender 
when  the  normal  condition  of  that  organ  is  disturbed." 

(i)  The  maxillary  incisors  refer  their  sensations  to  the  fronto-nasal 
area.  This  is  a  racquet-shaped  patch  extending  from  two  to  two  and 
a  half  inches  above  the  root  of  the  nose,  to  the  junction  of  the  hairy 


THE  NERVOUS  SYSTEM 


243 


scalp  with  the  forehead,  in  a  vertical  direction,  and  horizontally,  at  the 
level  of  the  eyebrow,  to  a  spot  three-quarters  or  one  inch  outwards  from 
the  median  line  of  the  face.  It  passes  down  the  side  of  the  nose  and 
terminates  at  the  upper  part  of  the  alee  nasi.  The  midline  is  unafifected. 
The  "maximum  point"  of  intensity  is  over  the  orbital  ridge  of  the 
frontal  bone,  at  a  spot  about  half  an  inch  from  the  median  line. 


Fig.  240 


The  fronto-nasal  area  (maxillary  incisors). 
In  this  and  the  succeeding  figures,  the  "maxi- 
mum spots"  are  indicated. 


The  nasolabial  area.     (Maxillary    canine    and 
first  premolar.) 


{ii)  The  maxillary  canine  and  first  premolar  refer  to  the  same 
area,  viz.,  the  naso-labial  area,  that  is,  over  the  upper  lip,  tip,  and 
under  surface  of  the  nose  and  on  the  cheek,  including  a  portion  also  of 
the  lower  lip,  extending  outwards  to  a  line  dropped  from  the  external 
canthus  of  the  eye. 

{Hi)  The  second  upper  premolar  may  refer  either  on  to  the 
temporal  or  maxillary  areas.  Of  these,  the  former  occupies  a  position 
over  the  temporal  fossa,  above  a  line,  three  or  four  inches  long,  uniting 
the  external  canthus  of  the  eye  with  the  upper  part  of  the  insertion 
of  the  ear,  its  anterior  border  being  three  inches  from  the  middle  line. 
The  "maximum  spot"  is  in  the  temporal  fossa,  immediately  above 
the  upper  border  of  the  zygoma. 


244 


THE  RELATIONSHIPS  OF   THE  TEETH  OF  MAN 


{iv)  Of  the  latter,  the  maxillary  area  is  associated  with  disturbances 
of  the  first  maxillary  molar  and  hard  palate,  as  well  as  the  premolar 
referred  to.  It  lies  over  the  maxilla  as  far  forwards  as  the  lateral  fold 
between  the  nose  and  the  cheek.  The  upper  border  corresponds  to 
the  lower  orbital  margin,  the  lower  border  to  a  curved  line  joining  a 
point  on  the  cheek,  close  to  the  fold  between  the  alae  of  the  nose  and 
the  upper  lip,  with  a  point  immediately  posterior  to  the  bony  orbit. 
Its  apex  is  placed  about  three  inches  from  the  median  line  of  the  face 
on  a  level  with  the  eyebrow. 


Fig.  252 


The  temporal  area.     (Maxillary  second 
premolar.) 


The  maxillary  area.     (Maxillary  second 
premolar  or  first  molar.) 


iv)  The  second  and  third  upper  molars  refer  on  to  the  mandibular 
area.  This,  roughly  triangular  in  shape,  lies  over  the  coronoid  process, 
the  ramus,  and  part  of  the  body  of  the  mandible.  It  includes  the  tragus 
of  the  ear,  the  "maximum  point"  being  placed  in  front  of  the  tragus, 
and  extends  as  far  forwards  as  a  line  dropped  vertically  from  the 
external  canthus  of  the  eye. 

{vi)  The  Mental  area  is  associated  with  disturbances  of  both  the 
mandibular  incisors,  canines,  and  first  premolar.  It  covers  a  surface 
of  which   the  upper  border  slopes  backwards  from   the  angle  of  the 


THE  NERVOUS  SYSTEM 


245 


mouth  to  a  line  dropped  vertically  from  the  external  canthus.  The 
lower  lip,  not  the  point  of  the  chin  is  included.  It  crosses  over  the 
lower  border  of  the  body  of  the  mandible  as  far  as  the  fold  which 
separates  the  chin  from  the  neck.  The  "maximum  spot"  is  situated 
over  a  line  dropped  from  the  angle  of  the  mouth,  /.  c.,  close  to  the 
orifice  of  issue  of  the  mandibular  nerve  through  the  mental  foramen. 
A  portion  of  the  anterior  surface  of  the  tongue  may  be  similarly 
tender. 


Fig.  254 


The  mandibular  area.     (Maxillary  second  and 
third  molars.) 


The  mental  area.     (Mandibular  incisors, 
'canine  and  first  premolar.) 


(vii)  The  second  lower  premolar  refers  to  the  mental  or  the  hyoid 
area.  The  latter  is  placed  partly  over  the  ramus  of  the  mandible, 
and  partly  behind  its  posterior  border.  It  extends  up  to  the  mastoid 
process  of  the  temporal  bone,  and  the  lobule,  but  not  the  tragus  of 
the  ear.  Here  there  may  be  two  maxima:  one  situated  below  the 
angle  of  the  mandible,  the  other  in  the  external  auditory  meatus, 
which  gives  rise  to  "earache." 

[viii)  The  first  and  second  mandibular  molars  refer  to  the  hyoid 
area. 


246 


THE  RELATIONSHIPS  OF   THE   TEETH  OF  MAN 


(ix)  The  lower  third  molar  may  produce  a  tenderness  of  the  skin 
over  the  superior  laryngeal  area.  Triangular  in  shape,  its  apex  lies  at 
a  spot  which  is  level  with  a  line  dropped  vertically  from  the  posterior 
attachment  of  the  ear.  The  posterior  part  of  the  lower  border  lies 
just  behind  the  front  border  of  the  sternomastoid  muscle,  and  passes 
forwards  to  a  level  of  the  lower  part  of  the  thyroid  cartilage.  The 
upper  border  embraces  the  fold  between  the  skin  and  the  neck. 
The  "maximum  point"  is  on  the  anterior  border  of  the  sternomastoid 
at  the  level  of  the  foramen  Adami. 


Fig.  255 


Fig.  256 


The   liyoid    area.     (Mandibular    second    pre- 
molar, and  first  and  second  molars.) 


The  superior  larjmgeal  area.     (Mandibular 
third  molar.) 


It  is  important  to  note  that  these  areas  do  not  correspond  with  the 
distributions  of  the  peripheral  branches  of  nerves  lying  over  the  face. 


THE    VASCULAR    SYSTEM 


The  pulps  and  alveolar  sockets  of  the  teeth  are  supplied  by  the 
internal  maxillary  artery.  The  maxillary  incisors  and  canines  are 
supplied  by  the  anterior  dental  branch,  running  in  the  anterior  dental 


THE  LYMPHATIC  SYSTEM  2A1 

canal  of  the  infra-orbital  division  of  the  third  stage  of  the  internal 
maxillary  artery. 

The  premolars  and  molars  are  supplied  by  the  posterior  dental 
artery,  from  the  third  stage  of  the  same. 

The  mandibular  incisors  and  canine  obtain  their  vascular  supply 
from  the  incisive  branch  of  the  inferior  dental  artery  and  the  premolars 
and  molars  from  the  inferior  dental  artery  itself. 

It  must  be  remembered  that  the  blood  supply  of  the  teeth  them- 
selves— as  apart  from  the  periodontal  membrane — is  very  peculiar. 
Not  only  is  there  no  collateral  circulation  amongst  the  arteries,  and 
the  veins  are  non-collapsible  and  valveless  as  described  elsewhere,^ 
but  in  addition  and  more  important  still,  as  age  advances,  the  blood 
supply  becomes  materially  diminished  on  account  of  the  closure  of 
the  apical  foramina.  This  closure  and  often  complete  obliteration 
seriously  menaces  the  life  histor^^  of  the  pulp.  In  the  opinion  of  the 
writer  the  pulps  of  people  over  thirty  years  of  age  begin  to  undergo 
degenerative  changes,  through  the  diminished  nutrition  on  the  part 
of  the  blood. 

Instances  often  occur  where  nerve  pains  in  teeth  (odontalgia)  are 
ascribed  to  a  faulty  metabolism  on  the  part  of  the  nerves  themselves. 
In  the  pulp  an  elevation  of  the  blood  pressure  or  a  chemical  change  in 
the  haemal  constituents  will  produce  pain  of  a  very  intractable  type, 
and  be  a  source  of  great  anxiety  to  the  practitioner,  whether  he  be 
in  dental  or  general  practice.  This  vascular  factor  must  never  be 
forgotten  in  the  solution  of  problems  of  odontalgia  of  a  complex 
and   obscure  character. 


THE    LYMPHATIC    SYSTEM 

The  submaxillary  lymphatic  glands  are  situated  in  the  submaxillary 
region,  and  some  of  them  are  imbedded  in  the  gland  of  that  name. 
The  lymphatics  of  the  cheek  and  face  and  parotid  glands  drain  into 
them,  also  those  from  the  submaxillary  and  sublingual  glands,  floor 
of  the  mouth,  and  anterior  part  of  the  tongue. 

The  deep  lymphatics  of  the  orbits,  nasal  fossae,  temporal  and  z^go- 


248 


THE  RELATIONSHIPS  OF   THE  TEETH  OF  MAN 


matic  fossae,  palate  and  cheek,  drain  into  the  internal  maxillary  lym- 
phatic glands  beneath  the  parotid  and  the  ramus  of  the  mandible. 

All   of   them   discharge    their   streams    into    the   superficial   cervical 
glands,  which  accompany  the  external  jugular  vein,  and  into  the 
cervical  glands  which  accompany  the  internal  jugular  vein. 


Fig.  257 


The  surface  markings  of  the  h-mphatie  system  of  the  face  and  neck,  showing  tlie  superficial  glands 
in  white,  in  the  cheek,  the  sub-maxillary,  sub-mental,  anterior  and  posterior  auricular,  and  supra- 
clavicular regions,  and  those  lying  on  the  sternocleidomastoid  muscle;  and  in  black,  the  deep  lym- 
phatics along  the  carotid  sheath  beneath  the  sternocleidomastoid  muscle. 


In  this  way  carious  teeth  in  the  mouths  of  weak  debilitated  children 
will  at  times  be  associated  with  enlarged,  indurated  submaxillary 
glands  and  cervical  glands,  in  much  the  same  way  as  with  enlarged 
tonsils  and  adenoids.  It  would  appear,  however,  that  enlarged  tonsils 
and  the  presence  of  adenoids  are  much  more  frequently  the  cause  of 
glandular  enlargement  than  are  carious  teeth. 

Cases  of  carcinoma  of  the  soft  palate  are  associated  with  enlarge- 


THE  LYMPHATIC  SYSTEM  249 

meat  of  the  glands  beneath  the  sternomastoid,  as  are  also  sarcomata 
of  the  tonsils — one  of  the  few  instances  where  this  form  of  malignant 
disease  is  disseminated,  not  through  the  ^'ascular  s}-stem,  as  usually 
is  the  case,  but  by  means  of  the  lymph  stream  itself. 

Referenxes 

1.  Choquet.    "Precis  d'Anatomie  Dentaire,  "  1903. 

2.  Dieulafe  and  Tournier.    "Evolution  de  la  voute  palatine,"  Bibl.  Anal.,  1908. 

3.  Grevers.     " Odontharmosi= :  a  Classification  of  the  Various  Forms  of  Occlusion  of  the  Teeth." 
The  Dental  Cosmos.  1905. 

4.  Head.    "Distribution  of  Sensation  with  Especial  Reference  to  the  Pain  of  Visceral  Diseases," 
Brain,  Part  III,  1894. 

5.  Hopewell-Smith.     "Pathology  of  the  Dental  Pulp"  in  "A  System  of  Dental  Surgery,"  edited 
bj'  Norman  G.  Bennett,  1912. 


THE  HARD   TISSUES  251 


THE    HARD    TISSUES 

The  bone  of  the  jaws  in  which  the  teeth  of  Man  are  implanted  are 
the  alveolar  processes  of  the  maxillae  and  mandible.  These  processes 
differ  from  those  of  the  majority  of  other  bones  in  that  they  afford 
no  muscular  attachment — the  main  function  of  bones — with  the  ex- 
ception of  some  fibres  of  the  broad  buccinator  muscle,  which  arises 
from  that  part  of  the  alveolar  processes  which  is  associated  with  the 
molars.  It  is  I'epeatedly  declared  that  there  is  a  difference  between 
the  osseous  frameworks  of  the  two  jaws,  that  of  the  superior  being 
the  more  cancellous,  that  of  the  lower  being  the  more  compact  of  the 
two.  This  is  true  as  far  as  their  external  and  exposed  portions  are 
concerned,  (^ompact  bone  forms  a  somewhat  thicker  shell  on  the  outer 
and  inner  surfaces  of  the  mandible  than  in  any  portion  of  the  maxillae. 
But  those  parts  in  closer  apposition  to  the  necks  and  roots  of  teeth 
are  essentially  and  fundamentally  the  same. 

Peripherally  placed  on  the  main  portion  of  the  maxillary  and  man- 
dibular bones,  and  each  affording  attachment  to  peripheral  bodies  like 
the  teeth,  which  possess  peripheral  structures — the  terminal  branches 
of  the  internal  maxillary  artery  and  fifth  pair  of  nerves,  and  the  com- 
mencing twigs  of  the  internal  maxillary  vein — the  naked  eye  and 
microscopical  characteristics  are  identical.  A  diploetic  tissue,  similar 
in  almost  all  points  to  that  cancellous  tissue  which  intervenes  between 
the  two  plates  of  the  cranial  bones,  such  as  the  parietal,  the  dense 
compact  structure,  in  normal  circumstances,  is  absent. 

The  author'  has  elsewhere  demonstrated  the  chief  histological  feat- 
ures of  these  bones,  and  has  pointed  out  in  what  ways  they  differ  from 
osseous  material  in  other  places.  It  may  be  recalled  that  in  the 
extremely  attenuated  bone  from  the  canine  fossa  of  the  upper  jaw, 
in  a  subject  of  ten  and  a  half  years,  the  tissue  is  scantily  supplied  with 
Haversian  systems,  portions  containing  no  lamellae  and  few  lacunae 
with  canaliculi,  the  matrix  being  coarsely  granular  Many  of  the 
lacunae  are  abrachiate,  like  those  occurring  in  the  bones  of  some 
fishes,   such  as  the  trout,  the  salmon,  the  cod,  and  grayling. - 

In  the  interdental  septa,  the  lattice-like  nature  of  the  tissue  is  similar 


252  THE  GINGIVAL  REGION 

to  spongy  bone  in  the  carpus,  tarsus,  and  expanded  ends  of  tibia  and 
femur.  The  lamellae  are  disposed  in  lines  parallel  with  the  edges  of  the 
large  openings  in  the  bone,  which  are  filled  with  medullary  substance; 
and  in  the  alveolar  process,  the  cancellous  spaces  run  longitudinally 
in  the  same  direction  as  the  long  axes  of  the  teeth.  The  Haversian 
systems  and  lacunae  are  pronounced,  and  the  thin  peripheric  lamellae 
are  slightly  denser  than  in  other  parts.  The  free  rim,  however,  is  so 
thin  that  there  is  little,  if  any,  room  to  accommodate  any  medullary 
tissue  or  Haversian  canals.  It  has  thus  an  impoverished  blood  supply 
and  its  vitality  is  necessarily  very  low. 

The  importance  of  this  anatomical  feature  cannot  be  too  strongly 
insisted  upon.  The  condition  obtains  in  Man  and  can  also  be  seen 
in  vertical  sections  of  jaws  of  the  Anthropoidea  and  Carnivora,  when 
the  outer  alveolar  plate  has  been  chiselled  away.  The  extremity  of 
the  external  alveolar  plate  is  considerably  thinner  than  that  of  the 
internal  alveolar  plate  as  the  photograph  (Fig.  258)  discloses. 

The  significance  of  this  fact  will  be  at  once  appreciated  when  general 
disturbances  of  the  vascular  system,  or  general  marasmus,  or  marantic, 
or  senile  changes  are  or  begin  to  become  manifest. 

The  result  is  absorption  of  this  terminal  edge,  {i)  physiological  in 
the  case  of  old  age — an  elastic  term  not  necessarily  governed  by  the 
actual  number  of  years  of  the  individual,  and  («')  pathological,  due  to 
diseases  of  the  neighbouring  parts.  Most  animals  in  ferd  naturd  lose  • 
their  teeth  by  shedding,  through  this  physiological  absorption  of  their 
sockets;  Man,  too,  but  in  the  latter,  the  process  is  greatly  accelerated 
by  incipient  disease.  The  effects  of  civilization  have  not  only  been 
felt  by  the  teeth,  but  by  their  sockets  also. 

The  cancellous  nature  of  the  associated  bone,  and  its  relative  softness 
can  be  seen  in  Figs.  100  and  258.  The  difficulty  encountered  at  times 
in  the  extraction  of  teeth  is  often  due  to  a  sclerosis  and  consequent 
density  of  the  external  and  internal  alveolar  plates.  In  ordinary  cir- 
cumstances the  immediate  attachment  is  more  or  less  soft  and  fragile. 

Comparison  with  the  sockets  of  the  anthropoid  apes  and  the  Car- 
nivora is  of  great  value.  In  the  orang-outang,  for  instance,  the  diploetic 
tissue  is  similar  to  that  of  Man.  The  ape,  however,  is  a  vegetable 
feeder,  and  not  omnivorous  as  is  his  simian  descendant.     The  teeth 


THE  HARD   TISSUES 

Fig.  25,S 


253 


4-  ^;i~ ',:  \ 


Side  view  of  jaws  of  au  adult  man,  with  the  external  alveolar  plate  removed  to  show  the  cancellous 
character  of  the  bone  of  the  sockets.  X  to.  Cf.  also  Fig.  194.  The  premolars  are  the  homologues 
of  the  third  and  fourth  premolars  in  the  typical  mammalian  dentition. 

Fig.  259 


Side  view  of  jaws  of  an  adult  orang-outang,  with  the  roots  and  sockets  of  the  teeth  exposed  to  show 
the  cancellous  character  of  the  bone.      X  s. 


254 


THE  GINGIVAL  REGION 
Fig.  260 


Side  view  of  jaws  o£  a  hyana  (Hyana  crocuta).  X  i-  The  external  alveolar  plate  haslbeen 
removed  to  show  the  sizes  and  positions  of  the  roots  of  the  teeth  and  the  compact  nature  of  the 
bone  of  their  sockets. 


Fig.  261 


Jaws  of  a  Polar  bear  {Ursus  mariUmus),  the  external  alveolar  plate  having  been  removed  to  show 
the  cancellous  nature  of  the  sockets  of  the  teeth.  X  3.  Two  premolars  have  been  shed  from  the 
upper  and  three  from  the  lower  jaw. 


THE  HARD   TISSUES  255 

here,  although  socketed  in  cancellous  bone,  remain,  speaking  generally, 
throughout  the  life  of  the  animal. 

In  the  Carnivora  the  hardest  and  most  enduring  sockets  are  those 
of  the  hycena,  whose  food  is  exceedingly  tough,  and  requires  most 
efficient  organs  for  its  comminution.  The  Polar  bear — a  fish  eater — 
has  a  less  dense  alveolar  process,  as  suits  its  requirements;  while  those 
of  the  tiger,  lion,  and  cat  occupy  an  intermediate  position  in  the  scale 
of  density. 


Side  view  of  jaws  of  a  lion,  with  tlu  n  ■■  a    jih  1  sockets  of  the  teetli  exposed  to  show  the  cancellous 
character  of  the  bone.      X  I-     The  fourth  premolar  is  the  carnassial  tooth. 

"Recession  of  the  gums"  is  a  vulgar  way  of  expressing  the  physio- 
logical absorption  of  bone.  "Recession"  of  the  gums  per  se  does  not, 
and  cannot,  take  place.  It  is  the  natural  thing  in  Man  for  the  alveolar 
edge  to  become  lost.  If  the  crania  exhibited  in  Anatomical  Museums 
be  examined,  it  will  be  difficult  to  select  any,  except  in  the  young,  in 
which  the  bone  is  closely  applied  to  the  necks  of  the  teeth,  and  it  will 
be  easy  to  mistake  the  macroscopical  appearances  of  jaws  which 
show  so-called  early  stages  of  "pyorrhoea  alveolaris,"  for  those  in 
which,  in  all  probability,  there  were  no  evidences  of  disease  at  all. 
A  distinction  must  be  made  between  normal  and  diseased  conditions 
of  the  sockets. 


Fig.  263 


Fig.  264 


Radiograph  of    the-  normal   sockets  of    the 
incisors  of  a  man,  aged  about  forty  years. 

Fig.  265 


Radiograpli  of  the  normal  sockets  of  the 
mandibular  incisors  of  a  woman,  aged  twenty 
years. 

Fig.  266 


Radiograph  of  the  normal  sockets  of  the 
mandibular  molars  of  a  woman,  aged  twenty 
years. 

Fig.  267 


Radiograph  of  the  normal  sockets  of  the 
mandibular  incisors  of  a  man,  aged  nineteen 
years. 

Fig. 


Radiograph  of  the  normal  sockets  of  the 
maxillary  incisors  of  a  man,  aged  nineteen 
years. 

Fig.  268 


Radiograph  of  the  normal  sockets  of  the 
maxillary  premolars  of  a  man,  aged  nineteen 
years. 

Fig. 270 


Radiograph  of  the  normal  sockets  of  the 
mandibular  premolars  and  first  molar  of  a  man, 
aged  nineteen  years. 


Radiograph  of  the  normal  sockets  of  the 
mandibular  molars  of  a  man,  aged  nineteen 
years. 


THE  SOFT  TISSUES,   THE  GUM  AND  GINGIVAL   TROUGH  257 

Rontgen-ray  photography  is  of  great  vakie  in  determining  the 
amount  and  constitution  of  the  alveolar  process,  though  it  must  be 
admitted  there  are  differences  between  radiographs  and  radiographs. 
Properly  applied  photographic  films  on  development,  show  in  other- 
wise apparently  normal  mouths  this  loss  of  bone  in  individuals  of 
middle  age. 

The  osseous  foundations  of  the  human  gingival  region  are  exceedingly 
variable  and  weak. 


THE   SOFT  TISSUES,  THE  GUM  AND  GINGIVAL  TROUGH 

The  soft  tissues  include  the  gum  and  periodontal  membrane.  The 
gum  is  attached  to  the  cementum  at  the  cervical  margins  of  the  teeth; 
enamel  cannot  on  account  of  its  physical  properties  afford  this  attach- 
ment. The  gum  ought  to  be  af^xed  to  the  free  edge  of  the  cementum, 
but  it  varies  considerably  in  the  exact  site.  The  gum  overlaps  the 
necks  in  varying  degrees.  A  trough  is  produced  in  a  narrow  relatively 
deep  sulcus,  which  at  the  terminal  edge  is  closely  approximated  to 
the  teeth.  The  depth  of  the  gingival  trough  varies  in  different  individ- 
uals and  in  different  parts  of  the  mouth.  Normally  in  children  from 
six  to  twelve  years  of  age,  it  may  measure  2.5  mm.  to  4.5  mm.  in  depth. 
In  children  of  six  or  seven  years  old  when  the  first  maxillary  incisors 
have  only  been  erupted  a  few  weeks,  it  may  measure  5  mm.  and  more, 
for  here  the  period  of  complete  eruption  is  not  finished. 

This  sulcus  has  been  called  the  "gingival  space"  by  Black  and 
others,  but  it  is  not  in  reality  a  "space,"  at  all  events  in  an  academic 
sense,  when  the  word  is  employed  to  denote  the  "distance  between 
objects,"  "room,"  "largeness,"  etc.  A  trough — the  gingival  trough 
— implies  "a  long,  narrow  channel,"  a  "concavity  or  hollow."  The 
gingival  trough  is  found  in  reptiles  and  the  lower  mammals,  and  varies 
in  shape  and  depth.  Fig.  272  is  a  vertical  section  of  the  jaws  and  teeth 
of  the  alligator,  and  Figs.  273,  274,  and  275  that  of  the  deciduous  teeth 
of  the  cat. 

In  Man  the  gingival  trough  contained  bacteria  in  e^•ery  instance 
personally  investigated  by  the  author,  which  may  or  ma\-  not  be  of  a 
17 


258 


THE  GINGIVAL  REGION 


pathogenic  character — but  more  often  the  former.*  It  does  not  contain 
the  saHvary  corpuscles  mentioned  by  Black;  and  there  is  no  room,  at 
first,  for  the  lodgement  of  food.      It  is,  however,  a  potential  "pocket." 


Fig.  271 


Photomicrograph  of  the  gingival  trough  which  has  become  a  "pocket,"  from  a  tooth  affected 
by  "  pyorrhoea  alveolaris."      X  V- 

*  In  the  cultures  made  from  the  bacterial  contents  of  the  gingival  trough  of  the  normal  mouth  of 
a  woman,  aged  twenty,  there  were  found  a  Streptococcus  in  long  chains,  and  also  a  Gram-negative 
coccus  belonging  to  the  Micrococcus  catarrhalis  group  of  microorganisms.  It  is  unnecessary  to 
state  that  every  precaution  was  taken  to  prevent  the  employment  of  any  alien  bacteria  in  these 
preliminary  experiments. 


THE  SOFT   TISSUES,   THE  GUM  AND  GIXGIVAL   TROUGH 


259 


As  far  as  is  yet  ascertained,  in  Man  there  are  no  openings  into  the 
gingival  trough — no  ducts  of  glands.  It  is  bounded  internally  by  the 
free  surface  of  enamel,  and  perhaps,  at  times,  by  a  small  amount  of 

Fig.  272 


Photomicrograph  showing  ihe  gingival  trough  of  a  young  alligator.     X  'i'. 

the  exposed  surface  of  cementum,  and  externally  by  the  oral  epithelium 
— a  narrower  layer  than  usual  of  the  mucous  membrane.  At  its  base 
is  the  junction  of  the  two,  and  just  beneath  is  the  superficial  portion 
of  the  periodontal  membrane. 


260 


THE  GIXGIVAL  REGION 


The  latter  is  not  held  closely  to  the  gingival  and  dental  tissues  by 
a  so-called  ligament — the  circular  "dental  ligament"  of  Stohr.^  In 
Man  it  is  non-existent,   as  are  also  the  so-called  lymphatics  of  the 


The  gingival  region  of  a  cat. 


periodontal  membrane.  The  gum  is  freely  supplied  on  its  lingual 
aspect  with  many  mucous  alveolar  glands,  the  apertures  of  the  ducts 
of  which  open  near  the  gingival  trough.  The  author  has  not  yet 
found  mucous  glands  on  the  buccal  or  labial  aspect  of  the  mucous 


THE  SOFT   TISSUES,   THE  GUM   AXD  GIXGIVAL   TROUGH 


2(jl 


membrane.  In  a  piece  of  tissue,  8  mm.  in  length,  from  the  mandible 
of  a  man,  aged  forty-two  years,  removed  from  the  premolar  region, 
there  were  no  microscopical  evidences  of  glands  on  the  buccal  side 

Pig.  274 


Same  as  Fig.  273.      X   '  \" . 

of  the.  gum.  As  yet  the  whole  extent  of  the  tissue  has  not  been  sur- 
veyed, but  until  this  is  done  it  may  be  inferred  that  if  they  do  exist 
in  this  region  they  are  considerabh*  more  scantily  scattered  than  on 
the  lingual  side. 


262 


THE  GINGIVAL  REGION 

Fig.  275 


" 'f^;;' 


Same  as  Fig.  273.      X   -y-. 


References 

1.  Black.     "Periosteum  and  Peridental  Membrane,"  1887. 

2.  Catalogue  of  the  Physiological  Series  in  the  Museum  of  the  Royal  College  of  Surgeons  of 
England,  1900. 

3.  Hopewell-Smith.       "The  Histology  of   the  Maxillary  and    Mandibular  Bones,"    The   Dental 
Cosmos,  1 90 1. 

4.  Stohr.    "  A  Text-book  of  Histologjf, "  1901. 


PLATE    IV 


/./ 


A  Human  Skull   in   Norma  Occipitalis.     X  - 


CHAPTER    XIII 
THE   DEVELOPMENT   OF   THE   JAWS   AND   TEETH 

Early  Formation  of  the  Head  and  Face. — Ossification  of  the  Maxillae. — Of  the  Premaxilte. — Changes 
in  the  IMaxillae  Produced  by  Age. — Ossification  of  the  Mandible. — Various  Theories. — Changes 
in  the  Mandible  Produced  by  Age. — The  Growth  of  the  Deciduous  Teeth. — The  Growth  of  the 
Permanent  Teeth. 

The  earlier  stages  in  the  development  of  the  jaws  and  of  the  teeth 
differ  in  the  important  particular  that,  while  the  former  are  difficult, 
the  latter  are  easy  to  follow  and  describe,  the  former  more  uncertain 
than  the  latter,  probably  for  the  reason  that  reliable  material  for 
examination,  on  the  one  hand,  is  relatively  scanty,  and,  on  the 
other,  plentiful.  The  anatomy  of  the  human  embryo  has  been  largely 
studied  by  His,  Minot,  Kolliker,  KoUman,  Rabl,  Ecker,  Coste,  etc., 
and  thanks  to  their  researches,  observations,  and  published  works,  a 
certain  amount  of  knowledge  is  forthcoming  regarding  the  earliest 
formations  of  the  jaws. 

The  primitive  mammalian  embryo  consists  of  two  longitudinal 
folds  of  epiblast,  rising  upon  either  side  of  the  middle  line,  or  Medullary 
groove,  which,  growing  backwards,  meet  and  form  a  longitudinal  canal. 
The  cephalic  extremity  of  this  canal  becomes  dilated,  and  soon  expands 
into  three  enlargements  called  the  Primary  cerebral  vesicles. 

The  Primary  cerebral  vesicles,  which,  of  course,  are  hollow,  become 
twice  bent  forwards  on  their  longitudinal  axes,  and  of  these  the  lower 
or  anterior  goes  to  form  the  frontal  protuberance.  They  are  lined 
externally  and  internally  with  epiblast  cells,  while  between  the  two  a 
layer  of  mesoblast  spreads  itself  over  the  whole  surface.  The  external 
layer  becomes  eventually  the  superficial  epithelium  of  the  scalp,  the 
internal  layer  the  nervous  system  of  the  encephalon,  and  the  middle 
mesoblastic  layer  gives  rise  to  the  dermis,  the  cranial  bones,  the  cerebral 
meninges,  muscles,  blood  vessels,  etc. 

The  Notochord,  or  Chorda  dorsaHs,  is  a  rod-shaped  column  of  cells, 


264  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

arising  from  the  hypoblast  at  the  anterior  end  of  the  "primitive  trace" 
of  the  embryo.  It  extends  from  the  cephahc  to  the  caudal  extremities, 
and  its  place  will  be  subsequently  occupied  by  the  bodies  of  the  ver- 
tebrae. Its  cephalic  termination  ends  in  a  mass  of  tissue  which  becomes 
cartilaginous,  and  gives  origin,  in  the  middle  line,  to  the  basi-occipital 
and  basi-sphenoid  bones,  and  laterally,  each  of  the  occipital  bones, 
the  greater  wings  of  the  sphenoid,  and  the  cartilage  surrounding  both 
primary  auditory  vesicles.  From  the  front  of  this  mass,  two  lateral 
bars  are  developed,  called  the  Trabecidce  cranii,  which  grow  in  a  forward 
direction  and  soon  coalesce  with  each  other.  From  this,  a  process, 
the  Fronto-nasal  process  arises,  and  becomes  prolonged  downwards 
ultimately  to  form  part  of  the  framework  of  the  face. 

Fig.  276 


M.N.R 


Diagram  of  the  head  of  an  embryo  of  about  four  weeks.  (After  His.)  Mx,  the  right  maxillary- 
process;  Mil,  the  mandibular  arch;  M.N.P.,  the  globular  extremity  of  the  mesial  nasal  process; 
H.A.,  hyoidean  arch;  F.B.A.,  the  first  branchial  arch;  E,  the  eye. 

The  face  is  formed  by  the  development  of  a  series  of  five  arches  of 
soft  tissue  separated  by  clefts.  The  arches  may  be  divided  into  two 
groups,  one  the  Pre-oral,  the  other  the  Post-oral,  so-called  from  their 
position  with  regard  to  the  buccal  cavity.  Of  these,  the  former  unites 
with  the  Fronto-nasal  process — which,  as  already  noted,  is  derived  from 
a  coalescence  of  the  Trabeculce  cranii — and  consists  of  three  plates, 
one  central  and  two  lateral.  The  central  is  named  the  Mid-frontal 
process.  From  it  the  nasal  septum  is  developed.  The  lateral  plates, 
separated  from  the  vertical  one  by  deep  furrows  (the  Primary  nasal 
fossce),  project  downwards  in  a  direction  parallel  with  the  Mid-frontaf 


THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH  2G5 

process,  and  then,  curving  towards  the  middle  Hne,  meet  with  the  Mid- 
frontal  process,  and  so  isolate  the  nasal  fossae  from  the  other  parts  of 
the  face.  The  lateral  plates  give  origin  to  the  lateral  portions  of  the 
ethmoid  and  lachrymal  bones,  and  by  joining  up  with  the  extremity 
of  the  Mid-frontal  process  form  the  central  part  of  the  upper  lip  and 
the  Premaxillary  bone. 

Fig.  277 


The  same  as  the  preceding  figure,  at  a  later  stage  of  development.  Viewed  from  below.  Mx., 
the  maxilla;  Mn.,  the  mandible;  F.N. P.,  the  fronto-nasal  process;  P.G.,  the  processus  globularis; 
L.N. P.,  the  lateral  nasal  process;  H.A.,  the  hyoidean  arch;  E.,  the  eye. 

The  Maxillary  processes  arise  from  the  parts  situated  behind  the 
Fronto-nasal  process,  and  are  associated  with  the  Post-oral  or  First 
visceral  arch.  Descending  for  a  short  distance,  they  form  the  external 
wall  of  the  orbit,  and  also  its  floor,  by  passing  inwards  and  meeting  the 
lateral  plates  of  the  Fronto-nasal  process.  Extending  farther,  in  an 
inward  and  downward  direction,  they  join  the  Mid-frontal  process,  and 
with  it,  complete  the  alveolar  arch  and  the  maxillary  bones.  Exten- 
sions of  the  inner  margins  of  this  arch,  on  either  side,  produce  the 
Palatal  processes,  which,  coalescing  in  the  middle  line,  form  the  vault 
of  the  palate.  In  front  they  do  not  unite,  but  leave  a  permanent 
lacuna,  which  eventually  becomes  the  anterior  palatine  foramen. 

Of  the  post-oral  arches,  the  first  is  concerned,  perhaps  about  the 
twentieth  day  of  intra-uterine  life,  with  the  production  of  the  Man- 
dibular arch,  and  contains  Meckel's  cartilage;  and  between  it  and  the 


266  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

Pre-oral  arch  the  buccal  cavity  is  formed,  which  thus  consists  of 
mesoblastic  tissue,  having  a  layer  of  epiblast  on  its  inner  surface. 
An  involution  of  epiblast  occurs,  which  elongates  until  it  comes  into 
contact  with  the  upper  part  of  the  alimentary  canal ;  the  intervening 
tissue — all  the  layers  of  the  primitive  blastoderm — soon  becomes 
absorbed,  and  the  mouth  {stomodceum)  and  alimentary  tract  become 

one  continuous  canal. 

Fig.  278 


The  same  at  a  later  stage,  showing  the  roof  of  the  mouth;  the  mandible  has  been  removed  in  order 
to  display  more  clearly  the  parts.    Lettering  as  before,  M.N. P.,  mid-nasal  process. 

To  recapitulate: 

(i)  The  premaxillary  bone  is  developed  by  the  union  of  the  mid- 
frontal  process  with  the  lateral  plates  of  the  fronto-nasal  processes: 

(ii)  The  palate  and  (iii)  maxillary  bones,  from  the  coalescence  of 
the  palatal  portions  of  the  maxillary  process  of  the  first  visceral  arch, 
with  the  mid-frontal  process,  and 

(iv)  The  mandible  from  the  first  post-oral  arch. 

About  the  twenty-ninth  day  of  intra-uterine  life  the  embryo  measur- 
ing 7.5  mm.  in  the  vertex-breech  diameter,*  the  mouth  is  a  wide  cavity 
having  in  front,  the  fronto-nasal  process,  behind,  the  mandibular  arches, 
and  on  each  side,  the  lateral  processes,  called  the  maxillary  processes 
which  project  forwards  between  the  optic  vesicles  and  mandibular 
arches. 

At  the  fourth  week,  the  lateral  and  mesial  nasal  processes  appear; 
these  were  originally  the  furrows  between  the  olfactory  pits. 

At  the  eighth  week,  the  embryo  measuring  30  mm.,  the  ossification 
of  the  maxillae  begins. 

*  In  foetuses  which  measure  from  lOO  to  220  mm.  the  vertex-breech  millimetre  length  equals 
approximately  their  age  in  days. 


OSSIFICA  TIOX  267 

OSSIFICATION 

The  ossification  of  the  jaws  begins  at  an  extremely  early  age,  that 
of  the  mandible  commencing  before  that  of  the  maxilla.  Of  all  the 
bones,  the  mandible  is  the  second  to  begin  to  be  formed,  the  first 
being  the  clavicle,  and  the  upper  jaw  the  third. 

The  details  of  development  have  been  studied  and  described  in  Great 
Britain,  among  others  by  Callender,=  Humphry,"  Parker, '^  Bland- 
Sutton, ^  Thane,--  Low,'"  and  Fawcett;^  in  France  by  Magitot,"  Mas- 
quelin,^-  Testut,-i  Julin,'*  Rambaud  and  Renault;^''  in  Germany  and 
elsewhere  by  Kerckring,"  von  Bardeleben,^  Baumiiller,-  Strelzoff,-" 
Schaffer,''  Spix,'"  Meckel,"  Mies,!'  Toldt,^'  and  Wolff.-^ 

Maxilla. — It  is  uncertain  from  how  many  centres  the  bone  is  ossified. 
They  are  deposited  in  membrane,  and  the  method  of  deposition  of 
calcific  material  is  similar  to  that  of  intra-membranous  ossification 
of  bone  in  other  parts.  They  appear  in  embryos  of  30  mm.  About 
the  tenth  week,  there  are  two  portions  of  the  bone — one  the  maxilla 
proper,  the  other  the  premaxilla.  The  intermaxillary  suture  persists 
till  adult  age,  but  does  not  pass  on  to  the  facial  surface,  probably 
because  the  anterior  wall  of  the  sockets  of  the  incisors  is  formed,  not 
by  the  premaxilla,  but  by  an  outgrowth  from  the  facial  portion  of  the 
maxilla  proper. 

The  antrum  of  Highmore  is  developed  at  an  earlier  period  than 
any  other  of  the  accessory  nasal  sinuses.  It  makes  its  appearance 
as  a  shallow  groove  on  the  inner  aspect  of  the  cartilaginous  nasal 
capsule,  about  the  fourth  month  of  intra-uterine  life,  and  enlarges 
continuously  until  after  the  completion  of  the  permanent  dentition. 

Areas  of  Ossification. — According  to  Schafer^"  there  are  six  areas 
of  ossification,  as  follow: 

(/)  The  Orbito-nasal  centre — situated  in  that  portion  of  the  body 
of  the  bone  which  lies  internal  to  the  infra-orbital  canal,  and  includes 
the  inner  part  of  the  floor  of  the  orbit,  and  the  outer  wall  of  the  nasal 
fossa ; 

{ii)  The  Malar  or  zygomatic  centre — which  forms  that  part  which 
lies  external  to  the  infra-orbital  canal,  and  includes  the  zygomatic 
process; 


268  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

{Hi)  The  Palatine  centre — which  gives  origin  to  the  palatal  process 
posterior  to  Stenson's  canal  with  the  adjacent  part  of  the  nasal  wall; 

{iv)  The  Premaxillary  centre — forming  the  front  part  of  the  alveolar 
process  which  has  the  incisors  implanted  in  it,  and  is  the  homologue 
of  the  premaxillary  bone  in  the  lower  vertebrates; 

{v)  The  Nasal  centre — which  gives  origin  to  the  frontal  process 
and  bone  above  the  canine;  and 

{vi)  The  Infra-vomerine  centre — which  lies  between  the  palatine 
and  premaxillary  areas,  and  beneath  the  vomer.  This  centre,  together 
with  the  corresponding  centre  in  the  bone  of  the  opposite  side,  separates 
the  foramina  of  Stenson  from  each  other. 

These  centres  are  supposed  to  appear,  as  already  noted  in  embryos 
of  30  mm.  long,  about  the  sixtieth  day,  and  to  fuse  with  one  another 
from  the  seventieth  to  the  eightieth  day. 

On  the  other  hand,  an  alternative  theory  is  held^  that  each  maxil- 
lary bone  arises  from  one  centre  of  ossification  as  a  membranous  bone, 
which  is  situated  at  a  point  in  the  neighbourhood  of  the  canine  tooth 
germ,  external  to  the  cartilaginous  nasal  capsule. 

From  this  centre  three  processes  radiate,  viz.: 

ii)  A  Nasal  process  growing  upwards; 

(ii)  An  Alveolar  process  extending  downwards  and  thickened  at  the 
base  to  form  the  malar  process;  and 

(Hi)  A  Palatine  process,  developing  inwards.  The  alveolo-malar 
process  grows  backwards  and  becomes  bifurcated  to  allow  the  anterior 
dental  nerve  to  pass. 

The  external  alveolar  border  is  developed  from  cartilage,  being  ossified 
by  extensions  of  bone  from  the  main  mass:  the  internal  alveolar  plate 
appears  to  come  as  a  downgrowth  from  the  palatine  process. 

In  the  absence  of  further  research,  it  may  be  perhaps  concluded 
that  the  six  centres  of  ossification,  described  by  Schafer,  are  really  not 
separate  centres,  but  extensions  from  one  central  point  as  just  described. 

Changes  in  the  Maxilla  Produced  by  Age. — At  birth,  the  vertical 
diameter  is  less  than  the  transverse  or  antero-posterior.  The  body  of 
the  bone  consists  of  little  more  than  the  alveolar  process.  The  sockets 
of  the  dental  germs  reach  almost  up  to  the  floor  of  the  orbit.  The 
antrum  appears  as  a  slit-like  furrow  on  the  outer  wall  of  the  nose. 


OSSIFICA  TIOX 


269 


In  adtdt  life,  in  consequence  of  the  development  of  the  alveolar 
process,  and  enlargement  of  the  cubical  capacity  of  the  antrum,  the 
vertical  diameter  becomes  the  greatest  of  the  three. 

In  old  age,  the  vertical  diameter  becomes  diminished,  the  alveolar 
process  undergoes  physiological  absorption  and  the  teeth  are  shed. 
The  lower  portion  of  the  bone  becomes  contracted  and  diminished  in 
thickness. 

Fig.  279 


The  skull  of  an  adult  man  whose  teeth  show  marked  attrition  and  pigmentation.     X  i. 

The  Premaxillary  Bone. — Reference  to  Albrecht's  investigations  have 
already  been  made  (see  Chapter  III).  On  the  authority  of  Professor 
Fawcett,  as  well  as  others,  there  probably  is  in  Man,  only  one  centre 
of  ossification  for  each  bone. 

It  is  situated,  like  a  bridge,  over  the  interval  between  the  two  incisor 


270 


THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 


germs.  A  piece  of  the  outer  alveolar  border,  and  a  part  of  the  nasal 
process  are  formed  from  that  portion  of  it  which  is  near  the  second 
incisor. 

At  a  later  period  the  premaxilla  consists  of  two  parts:  {i)  A  Pro- 
cessus lateralis.,  or  facial  part,  and  [id)  a  Processus  medialis,  which  runs 
backwards  on  the  mesial  surface  of  Stenson's  foramen.  Still  later, 
two  wedge-shaped  processes  grow  backwards  from  the  facial  portion 


The  skull  of  an  aged  person 


to  meet  the  palatine  processes  of  the  maxilla  proper,  which  cause  the 
two  sutures  seen  on  the  under  surface  of  the  whole  bone.  Finally,  a 
downgrowth  of  bone  occurs. to  form  the  anterior  alveolar  wall,  and 
hides  from  view  the  two  incisors  and  the  anterior  dental  nerve. 

The  Mandible. — A  brief  resume  of  the  theories  held  by  the  most 
eminent  anatomists  regarding  the  ossification  of  this  bone  must  now 
be  given. 


OSSIFICATION 


271 


About  two  and  a  half  centuries  ago,  Kerckring"  studied  the  develop- 
ment of  the  mandible,  and  believed  that  the  coronoid  process  possessed 
a  separate  centre  of  ossification. 

Spix,'"  at  the  beginning  of  the  Nineteenth  Century,  added  a  fifth 
centre — "the  piece  of  Spix" — otherwise  the  Splenial  centre — to  the 
other  four  previously  described  by  Autenrieth,  viz.,  one  each  for  the 
coronoid  process,  the  condyle,  the  angle,  and  the  horizontal  portion 
of  the  body  of  the  jaw. 

Fig.  281 


The  same — side  aspect.      X  7. 

Meckel"  discovered  the  cartilage  which  bears  his  name,  in  1821; 
and  Callender''  was  the  first  to  show  that  this  cartilaginous  rod  becomes 
ossified.  To  this  portion  he  gave  the  name  of  the  Mento-Meckelian 
centre. 

Renault  and  Rambaud'^  describe  six  centres,  and  give  the  dates 
of  their  appearance  and  fusion. 


272  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

Bland-Sutton,^  in  1883,  described  six  centres — of  which  five  corre- 
sponded to  those  described  by  Spix,  the  sixth  representing  the  Mento- 
MeckeHan  of  Callender. 

The  following  drawing  from  his  paper  gives  the  positions  of  these 
centres: 

He  writes:  "So  far  as  I  have  been  able  to  observe,  the  nucleus 
marked  D  in  Fig.  282  is  the  first  to  appear;  from  this  centre  the  larger 
part  of  the  body  of  the  bone  is  formed.  At  first  it  resembles  a  shallow 
trough  lodging  the  cartilage. 


Diagram  of  the  centres  of  ossification  of  the  mandible  at  about  the  tenth  week  of  intra-uterine 
Hfe.  (After  Bland-Sutton.)  X  V".  4,  the  coronoid;  B,  the  condyle;  C,  the  angular;  D,  the  dentary; 
E,  the  Mento-Meckelian ;  F,  the  splenial  centre. 

"The  nuclei  for  condyle,  coronoid,  and  angle  follow  so  rapidly  that 
it  is  difficult  to  determine  their  order.  About  the  same  time,  osseous 
granules  may  be  seen  in  the  perichondrium  surrounding  the  distal 
end  of  Meckel's  cartilage,  gradually  invading  its  substance. 

"As  soon  as  the  various  centres  make  their  appearance,  a  thin  net- 
work of  osseous  tissue  quickly  connects  them.  When  this  occurs,  a 
thin  shelf  of  bone  will  be  found  immediately  above  Meckel's  cartilage 
and  the  inferior  dental  nerve.  This  latter  osseous  streak  lies  on  the 
inner  side  of  the  developing  bone,  quite  distinct  from  the  other  centres, 
and  represents  the  splenial.  Now  is  the  very  best  time  to  observe  the 
various  nuclei,  particularly  if  the  bone  is  rendered  transparent  by 
means  of  alcohol  and  oil  of  cloves.  Its  appearance  is  very  striking. 
The  bone  presents  the  familiar  shape  of  the  foetal  jaw,  but  its  texture 
reminds  one  of  a  spider's  web,  the  various  centres  showing  like  flies 
entangled  in  the  mesh. 

"The  order  of  events  may  be  arranged  in  stages  for  the  sake  of 
clearness  thus: 


OSSIFICATION  273 

"l.  Meckel's  cartilage  appears. 

"2.   Dentary  is  seen  below. 

"3.  Centres  for  condyle,  coronoid,  angle,  and  Mento-Meckelian. 

"4.  Network  of  osseous  tissue  connects  them  together. 

"5.  Splenial  appears  as  ledge  of  bone  supporting  teeth. 

"6.  Disappearance  of  Meckel's  cartilage  from  jaw,  and  fusion  of 
splenial. 

"The  splenial  element  is  interesting  on  account  of  its  relation  to 
the  developing  teeth.  On  its  first  appearance  it  stands  out  at  right 
angles  to  the  dentary,  serving  to  separate  the  teeth  germs  from  Meckel's 
cartilage.  If  at  the  fourth  month  of  intra-uterine  life  the  tissues  on 
the  inner  side  of  the  jaws  be  carefully  dissected  away  the  splenial 
will  be  observed  forming  a  distinct  ledge  of  bone,  supporting  on  its 
superior  surface  the  dental  follicles  like  flasks  on  a  shelf;  immediately 
beneath  it  runs  Meckel's  cartilage  and  the  nerve.  As  the  cartilage 
atrophies,  the  splenial  extends  downwards  to  fuse  with  the  dentary 
immediately  below  the  nerve;  in  this  way  the  mylohyoid  branch  gets 
shut  off  from  the  main  portion  of  the  inferior  dental  nerve.  After  the 
fourth  month  it  extends  vertically  to  form  the  inner  wall  of  the  maxilla, 
all  trace  of  its  originally  separate  condition  being  thus  completely 
lost,  the  bone  then  assuming  the  condition,  which  it  presents  at  birth, 
with  which  we  are  all  so  familiar. 

"Let  me  now  offer  evidence  of  a  different  character  of  the  com- 
pound nature  of  this  bone.  In  the  year  1814,  the  celebrated  French 
anatomist,  Serres,  in  a  paper  read  before  the  Academic  des  Sciences, 
Paris,  propounded  certain  laws  bearing  on  ossification.  Among  them 
was  one  termed  the  'Loi  de  Conjugaison,'  by  which  he  showed  the 
various  foramina  in  bones  to  result  from  the  opposition  of  two  or  more 
•distinct  bones  or  distinct  centres  of  ossification.  To  this  law  there 
were  many  exceptions;  among  the  more  unstable  were  certain  fora- 
mina in  the  temporal  bone  and  the  inferior  dental  foramina. 

"When  I  first  took  up  the  subject  of  nerve  foramina,  Serres'  re- 
searches were  quite  unknown  to  me,  and  I  took  as  m>"  guide  this  rule: 
'Whenever  a  nerve  passes  through  a  bone  it  marks  the  confluence  of 
two  or  more  ossific  centres.'  Among  the  earliest  bones  to  yield  under 
this  method  of  analysis  were  the  temporal  and  the  inferior  maxilla; 


274  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

later  I  became  acquainted  with  Serres'  paper,  the  greater  part  of  which 
is  pubHshed  as  a  footnote  in  the  French  translation  of  Meckel's 
'Anatomic  Comparee,'  vol.  iv.  Much  to  rfiy  satisfaction  I  found  that 
my  method  had  yielded  far  more  satisfactory  results  and  had  banished 
two  of  the  apparently  most  obvious  exceptions  to  the  law,  and  it  is 
most  interesting  to  trace  out  the  intricate  pathways  by  which  many 
nerves  quit  the  cranial  cavity  in  order  to  avoid  piercing  an  ossific 
centre. 

"Applied  to  the  lower  jaw,  the  rule  stands  thus:  The  nerves  con- 
cerned are  the  inferior  dental,  mental,  and  mylohyoid.  The  inferior 
dental  enters  by  the  foramen  of  the  same  name,  formed  by  the  coales- 
cence of  the  coronoid,  condyloid,  dentary,  angular,  and  splenial  ele- 
ments; the  nerve  then  travels  in  a  tunnel  formed  on  the  outer  side 
of  the  dentary  and  on  the  inner  side  of  the  splenial.  The  mental 
branch  passes  out  through  a  fenestrum  formed  by  dentary  and  Mento- 
Meckelian  ossification. 

"The  mylohyoid  runs  in  the  groove  which  once  lodged  Meckel's 
cartilage,  the  sulcus  also,  corresponding  to  the  junction  of  splenial 
with  dentary.  As  the  inferior  dental  passes  along  the  canal,  it  sends 
up  twigs  to  the  teeth,  and  these  twigs  occupy  foramina  or  spaces 
between  the  splenial  and  dentary.  The  relation  of  nerves  thus  lends 
additional  help  in  unravelling  the  mystery." 

Bland-Sutton,  from  this  point,  proceeds  to  the  comparative  side 
of  the  question,  quoting  the  condition  in  the  dog-fish,  the  sturgeon, 
the  amia,  the  cod,  amphibia,  and  reptiles.  He  finally  gives  a  table  of 
homologies  thus: 

Man.  Fish. 

The  Mento-Meckelian  is  the  homologue  of  the  Mento-Meckehan. 

The  Angle  corresponds  with  the  Angular. 

The  Condyle  corresponds  with  the  Articular. 

The  Coronoid  correspondswith  the  Surangular. 

The  Splenial  corresponds  with  the  Splenial. 

The  Dentary  corresponds  with  the  Dentary. 

The  latest  investigations  in  this  subject  are  those  of  Professor 
Fawcett  and  Mr.  Low.  Curiously  coincidental — although  the  research 
was  carried  on  entirely  independently — they  were  published  more  or 


OSSIFICATION  275 

less  simultaneously,  and  they  are  so  much  alike  that  they  are  accepted 
by  such  an  authority  as  the  editor  of  Gray's  Anatomy. 

Fawcett's  Summary. — "First. — The  jaw  in  its  ossification  is  not 
so  complex  as  some  would  have  us  think,  but  it  is,  for  all  that,  complex, 
involving  (a)  Meckel's  cartilage  at  its  anterior  extremity;  (b)  the 
membrane  on  the  outer  side  of  Meckel's  cartilage;  and  (c)  at  least  one 
accessory  cartilage  which  is  found  in  the  condyle,  neck,  and  base  of 
the  coronoid  process  of  the  jaw.  These  statements  apply  to  each  half 
of  the  jaw. 

"Second. — In  order  of  sequence,  ossification  occurs  first  in  the 
membrane  between  the  mental  nerve  and  the  middle  line,  and  extends 
backwards  under  the  mental  nerve.  Next,  ossification  commences  in 
Meckel's  cartilage,  about  the  tenth  week  of  foetal  life,  in  the  region 
of  the  mental  foramen,  and  gradually  extends  inwards.  That  part  of 
the  jaw  then  between  the  mental  foramen  and  the  symphysis  is  com- 
pound in  origin,  being  partly  cartilaginous,  partly  membranous, 
not  entirely  cartilaginous,  as  Bland-Sutton  says.  Finally,  ossification 
takes  place  in  the  accessory  mass  of  cartilage  in  the  condyle  and  the 
root  of  the  coronoid  process  at  the  third  month. 

"  Third. — There  are  no  separate  centres  in  membrane  for  either 
the  coronoid  process,  or  for  the  angle,  or  the  so-called  splenial,  all  these 
parts  being  outgrowths,  as  it  were,  from  the  main  mass. 

"  Fourth. — The  inner  alveolar  border  is  developed  in  two  parts  by 
ingrowths  from  the  main  mass,  and  at  two  dififerent  periods,  viz.,  that 
part  behind  the  mental  foramen  appearing  first,  and  elongating  from 
before  backwards,  that  part  in  front  of  the  foramen  appearing  later 
and  growing  from  behind  forwards. 

"  Fifth. — The  canal  for  the  nerves  is  completed  by  the  growth  of 
spicules  of  bone  from  one  alveolar  border  to  the  other,  over  the  top  of 
the  nerves,  the  mental  nerve  being  first  so  covered,  then  the  incisive, 
and  much  later,  the  inferior  dental,  near  the  permanent  inferior  dental 
foramen. 

"Sixth. — The  sockets  of  the  teeth  become  bony  comparatively  late, 
that  of  the  canine  appearing  first. 

"Seventh. — Meckel's  cartilage  becomes  incorporated  in  the  jaw 
anteriorly   by   the   development  of   upper   and   lower  shelves,   which 


276  THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 

gradually  close  over  it;  behind  the  mental  foramen  these  shelves  do 
not  meet,  and  Meckel's  cartilage  is  consequently  not  included  in  the 
jaw,  but  gradually  atrophies. 

"Eighth. — I  do  not  think  that  Meckel's  cartilage  atrophies  to  form 
the  internal  lateral  ligament  of  the  jaw.  This  ligament  in  the  fourth 
month  can  be  seen  quite  distinctly  in  an  ordinary  dissection  to  be 
independent  of  Meckel's  cartilage." 

Low's  Conclusions. — The  above  description  corresponds  fairly 
closely  with  Low's  observations,  with  the  exception  that  the  latter 
author  describes  a  further  cartilaginous  patch  situated  on  the  anterior 
border  of  the  coronoid  process.  In  both  instances  serial  sections, 
and  not  clarified  specimens,  were  examined. 

Fig.  283 


Diagram  of  Meckel's  cartilage,  showing  its  association  with  the  malleus  at  its  posterior  extremity: 
M.C.,  Meckel's  cartilage;  Mn.,  mandible;  M..  malleus;  I.,  incus;  S.,  stapes. 

The  following  are  the  conclusions  arrived  at  by  Low: 

Each  half  of  the  mandible  is  developed  from  the  dentary  centre  in 
membrane;  the  splenial  centre  does  not  exist  separately,  but  is  really 
an  extension  of  the  dentary  which  goes  to  take  part  in  the  formation 
of  the  internal  alveolar  plate. 

Meckel's  cartilage  has  no  share  in  the  formation  of  the  bone  except 
towards  its  anterior  portion,  viz.,  that  situated  just  below  and  inside 
the  positions  occupied,  in  future,  by  the  sockets  of  the  first  and  second 
incisors.  Here  it  becomes  ossified  and  incorporated  with  the  mandible. 
The  extreme  front  terminations  of  the  cartilage  persist  throughout 
intra-uterine  life  as  one  or  more  cartilaginous  nuclei  or  nodules  behind 
the  symphysis;  these  extremities  never  fuse. 

At  a  somewhat  later  stage  certain  accessory  cartilaginous  nodules 
appear  in  connection  with  the  primary  membranous  bone.     A  condylar 


OSSIFICA  TION  277 

cartilage  and  a  smaller  coronoid  cartilage  are  well  defined,  as  also  are 
smaller  cartilaginous  nuclei  situated  "along  the  margins  of  both  alveolar 
walls  in  front  as  well  as  along  the  front  of  the  lower  border  of  the  jaw." 
They,  however,  are  not  separate  centres  of  ossification,  but  become  ossi- 
fied by  extension  from  the  growing  bone  around.  Apparent!}',  according 
to  this  author,  no  definite  cartilaginous  nucleus  for  the  angle  exists;  and 
there  is  only  one  centre  of  ossification,  viz.,  the  dentary  for  each  half  of 
the  bone. 

Changes  in  the  Mandible  Produced  by  Age. — At  birth  the 
bone  consists  of  two  lateral  halves,  joined  at  the  symphysis  by  fibrous 
membrane.  The  framework  of  the  body  is  very  thin  and  contains 
the  sockets  of  the  two  deciduous  incisors,  the  canine  and  the  two 
molars  in  each  half.  The  sockets  are  only  deep  enough  to  enclose  the 
partially  developed  teeth,  and  are  separated  by  imperfect  septa  of  bone, 
those  of  the  first  mentioned  being  wider  at  the  base  than  above. 

The  calcification  of  these  deciduous  teeth  has  usually  advanced 
so  far  as  to  form,  roughly,  half  the  crown  of  the  first  incisor,  one- 
fourth  of  that  of  the  second  incisor,  one-sixth  of  that  of  the  canine, 
the  whole  of  the  morsal  surface  of  the  first  molar,  and  the  united 
cusps  of  the  second  molar.  The  enamel  is  more  or  less  half  its 
ultimate  thickness. 

The  mandibular  canal,  large  in  size,  runs  near  the  inferior  border 
of  the  bone;  the  mental  foramen  opens  beneath  the  socket  of  the 
first  molar;  the  neck  of  the  condyle  is  short  and  about  on  the  same 
horizontal  plane  as  the  upper  portion  of  the  alveolar  process.  The 
coronoid  process  is  large,  and  situated  at  right  angles  to  the  body  of 
the  bone.    The  angle  is  obtuse  and  measures  about  175  degrees. 

After  Birth. — Union  of  the  lateral  halves  occurs  during  the  first 
year  post  natum.  The  body  undergoes  a  lengthening  and  a  deepening. 
The  former  takes  place,  chiefly,  in  that  part  behind  the  mental  foramen, 
for  the  accommodation  of  the  three  additional  permanent  molars;  the 
latter  in  two  directions:  (?)  In  the  alveolar  part,  to  allow  for  room 
for  the  growth  of  the  roots  of  the  deciduous  teeth,  and  the  crypts  of 
their  permanent  successors;  and  (?'/)  by  additions  to  the  anterior  or 
sub-dental  portions  for  the  attachment  of  the  muscles  of  mastication. 
The  greater  part  of  the  body  now  lies  above  the  external  oblique  line. 


278  THE  DEVELOPMENT  OF   THE  JAWS  AND  TEETH 

After  the  second  dentition  is  completed,  the  orifice  of  the  mental 
foramen  is  situated  between  the  first  and  second  premolars;  the 
mandibular  canal  itself  lying  just  above  the  level  of  the  mylohyoid 
ridge.  The  angle  at  the  fourth  year  is  140  degrees,  and  the  alveolar 
arch  describes  a  segment  of  a  circle. 

In  adult  life,  both  alveolar  and  basal  portions  of  the  jaw  are  of 
equal  depth;  the  mandibular  canal  runs  parallel  with  the  mylohyoid 
ridge;  and  the  mental  foramen  opens  midway  between  the  superior 
and  inferior  border.  The  angle  approximates  now  90  degrees,  the 
ramus  being  nearly  vertical.    The  alveolar  arch  has  become  a  parabola. 

In  old  age  there  is  a  great  reduction  in  size,  through  the  shedding 
of  the  teeth  as  a  physiological  or  pathological  process.  The  result  is 
loss  by  absorption  of  the  alveolar  process.  The  greater  part  of  the 
bone  now  lies  below  the  oblique  line.  The  mandibular  canal  lies  close 
to  the  alveolar  body;  and  this  fact  probably  accounts  for  the  obscurity 
of  pains  which  sometimes  occur  in  edentulous  persons  who  are  wear- 
ing dentures.  The  neck  of  the  condyle  assumes  somewhat  the  infantile 
position,  being  bent  backwards;  the  angle  is  again  slanting  (nearly 
170  degrees),  and  the  ramus  is  no  longer  vertical,  but  obliquely  placed 
with  regard  to  the  body  of  the  bone. 


THE    GROWTH    OF    THE    DECIDUOUS    TEETH 

The  various  stages  of  development  of  the  teeth  at  birth  have  already 
been  detailed.     It  now  remains  to  note  the  subsequent  changes. 

The  anterior  surfaces  of  the  maxillary  first  incisors  are  exposed 
through  absorption  of  their  crypt  walls  at  about  eight  and  a  half 
months  post  natum,  but  their  thin  incisive  edges  remain  at  a  level 
with  the  alveolar  margin,  while  they  themselves  occupy  a  slightly 
prominent  position  in  the  dental  arch.  The  second  incisors  are  placed 
in  a  circle  which  passes  behind  these  teeth,  and  also  the  canines  which 
are  still  enclosed  in  bone.  The  same  remark  applies  equally  to  the 
mandibular  series,  with  the  exception  that  the  second  incisors  are 
more  in  alignment  with  the  first.  The  crowns  of  the  latter  are  com- 
pleted and  their  cervical  constriction  beginning  to  be  manifest. 


THE.  GROWTH  OF   THE  DECIDUOUS   TEETH  279 

Fic.  284 


The  deciduous  teeUi  of  a  cliilJ.      X    :■ 
Fig.  285  Fig.  286 


Skull  of  a  child  at  fiirtli.      X 


The  same  at  a  later  period.      X  j-. 


280  THE  DEVELOPMENT  OF  THE  JAWS  AND  TEETH 

Fig.  287 


The  same  at  a  later  period.      X  ;■ 


The  same  at  a  later  period.     X  f . 


THE  GROWTH  OF   THE  DECIDUOUS   TEETH 


281 


The  molar  sockets  are  separated  from  the  floor  of  the  orbit  by  the 
rapidly  growing  antrum. 

Fig.  28 


The  same  at  a  later  period.     X  ". 
Fig.  290 


The  same  at  a  later  period.      X  '-■ 


282 


THE  DEVELOPMENT  OF   THE  JAWS  AND   TEETH 


About  the  thirteenth  month  the  maxillary  second  incisors  are  in 
place,  and  the  crowns  of  the  first  molars  beginning  to  emerge  from  the 
sockets;  about  five  weeks  later,  the  partially  complete  molars  are  in 
occlusion. 

About  the  fortieth  month,  the  incisors  are  completely  formed, 
the  canine  roots  are  as  yet  only  partially  developed,  the  first  molars 

Fig.  291 


The  same  at  a  later  period.      X 


are  one-fifth,  and  the  second  molars  are  half  of  their  normal  length, 
and  it  is  not  until  the  fifth  year  that  the  roots  of  all  the  deciduous 
teeth  are  fully  formed.  From  examinations  of  the  skulls  in  the  Royal 
College  of  Surgeons  Museum,  it  would  appear  that  by  the  third  year 
the  deciduous  dentition  is  complete  and  fully  erupted. 


THE  GROWTH  OF   THE  PERMANENT  TEETH 


283 


THE    GROWTH    OF    THE    PERMANENT    TEETH 

There  are  ten  anterior  successional,  and  six  posterior  non-succes- 
sional   teeth  in  Man. 

The  Successional  Series. — Close  before,  or  soon  after,  the  one  hundred 
and  seventeenth  day  of  intra-uterine  life,  the  enamel  organs  of  the 
permanent  incisors  and  canines  are  formed,  and  the  premolars  slightly 
later.  They  occupy  sites  on  the  lingual  side  of  each  deciduous  tooth 
germ.  Ten  in  number  in  both  maxillae  and  mandible,  it  is  established 
that    the    anterior    ones    precede    the    posterior    in    their    formation. 


Fig.  292 


Diagram  showing  the  changes  in  the  shapes  of  the  cavities  of  the  mandible  which  are  consequent 
on  the  growth,  the  teeth  of  the  permanent  dentition.  (After  Blake.)  .4,  B,  C,  before  the  shedding 
of  the  deciduous  teeth;  D  (a  lateral  view).  D.T.,  deciduous  tooth;  P.T.G.,  permanent  tooth  germ; 
I.D.,  iter  denlis. 

These  permanent  tooth  germs  rapidly  extend  downwards  or  upwards 
as  the  case  may  be,  into  the  soft  tissues,  acquire  dental  papillse  and 
become  enclosed  in  sacs  which  adhere  to  the  lingual  surfaces  of 
the  corresponding  deciduous  tooth  germs.  The  bone  of  the  jaw  sur- 
rounds both  the  milk  and  permanent  germs  and  provides  a  special 
cavity  on  the  lingual  side  for  the  reception  of  each  of  the  latter. 

Each  permanent  tooth  sac  soon  grows  some  distance  below  and  behind 
the  deciduous  tooth  germ;  is  at  first  pyriform  in  outline  and  after- 
wards becomes  connected  with  the  germ  by  a  solid  peduncle  of  con- 


284  THE  DEVELOPMENT  OF  THE  JAWS  AND  TEETH 

nective-tissue  fibres  (the  Gubernaculum) ,  which  Ues  in  a  long  bony- 
canal  {the  Iter  dentis) ,  whose  aperture  is  placed  behind  the  correspond- 
ing deciduous  tooth  (Fig.  292).  The  bony  partition  which  thus  inter- 
venes between  the  lower  part  of  the  deciduous  tooth  and  the  crown 
of  the  permanent  tooth  becomes  absorbed — probably  by  a  special 
absorbent  organ — as  the  crown  of  the  latter  rises  through  the  gum. 

The  sockets  of  the  permanent  teeth  are  formed  at  the  same  time 
as  the  roots  become  developed. 

The  Non-successional  Teeth. — The  six  permanent  molars  in  each 
jaw  arise  from  the  backward  extension  of  the  common  dental  lamina, 
the  anterior  part  of  which  has  already  produced  the  ten  deciduous 
teeth,  and  the  ten  successional  tooth  germs.  That  part  of  the  Zahn- 
leiste  which  runs  behind  the  second  deciduous  molar  remains  unobliter- 
ated  for  a  long  time,  till  about  the  one  hundred  and  twentieth  day  a 
special  enamel  organ  begins  to  appear  for  the  first  permanent  molar. 
During  the  fourth  month  after  birth  that  of  the  second  molar  is  similarly 
developed,  and  probably  about  the  third  or  fourth  year  that  of  the 
third  molar. 

Failure  of  atrophy  of  the  portions  of  the  tooth  band  which  inter- 
venes between  the  tooth  germs,  and  persistence  of  the  unabsorbed 
portions  may,  in  certain  circumstances,  produce  either  {i)  super- 
numerary teeth,  (??')  enamel  nodules,  [in)  true  gemination,  or,  at 
times,   iiv)   epithelial  odontomes. 

About  the  fortieth  month  the  permanent  incisors,  canines,  and 
first  molars  are  completed  as  far  as  their  crowns  are  concerned;  the 
earliest  traces  of  calcification  are  beginning  to  appear  in  the  first  pre- 
molars and  less  than  two  years  later  that  of  the  second  premolar. 

At  the  time  when  physiological  absorption  of  the  roots  of  the  decid- 
uous incisors  is  proceeding,  the  roots  of  the  permanent  incisors  have 
begun  to  develop,  the  crowns  of  the  canine  and  premolars  are  still 
incomplete,  the  roots  of  the  first  permanent  molars  are  undergoing 
completion,  while  the  crowns  of  the  second  molars  are  only  partially 
calcified. 

The  permanent  canines  at  nine  years  are  complete  as  far  as  half  the 
root  is  concerned,  and  at  twelve  the  calcification  is  practically  finished; 
of  the  first  premolars,  one-fourth  of  the  root  at  the  ninth  year  and  the 


THE  GROWTH  OF   THE  PERMANENT   TEETH  285 

whole  at  the  twelfth ;  of  the  second  premolar,  at  nine  years  the  commence- 
ment of  the  calcification  of  the  root  and  at  twelve  years  its  completion ; 
of  the  first  molar,  the  growth  of  the  roots  ceases  about  the  tenth  year; 
of  the  second  molar,  commencement  of  calcification  of  the  roots  is 
observed  and  not  completed  till  about  the  fifteenth  to  the  seventeenth 
year;  of  the  third  maxillary  molar,  at  about  twelve  years  the  crown  is 
more  or  less  calcified — the  mandibular  molar  is  less  advanced,  and 
growth  ceases  from  the  seventeenth  to  the  twenty-second  year. 

References 

1.  Von  Bardeleben.  "Der  Unterkiefer  der  Saugethiere,  besonders  des  Menschen,"  Anat. 
Anzeig.,  1805. 

2.  BaumuUer.  "Ueber  de  letzten  Veranderungen  des  Meckels'chen  Knorpels, "  Zeitschrifl  fiir 
luissen.  Zoblog.,  1879. 

3.  Bland-Sutton.     "Development  of  Inferior  Maxilla,"  Trans.  Odonio.  Soc.  Great  Brilain,  1883. 

4.  Brock.  "Ueber  die  Entwickelung  des  Unterkiefers  der  Saugethiere,"  Zeitschrift  fur  wissen. 
Zoologie,  1876. 

5.  Callender.  "The  Formation  and  Early  Growth  of  the  Bones  of  the  Human  Face,"  Phil. 
Trans.,  1869. 

6.  Fa'wcett.  "The  Ossification  of  the  Lower  Jaw  in  Man,"  Proc.  Anat.  Soc.  of  Great  Britain 
and  Ireland,  1904;  also  Journal  of  the  American  Medical  Association,  1905;  also  "Reconstruction  of 
the  Head  of  a  30  mm.  Human  Embryo, "  Anatom.  Anzeiger,  1910. 

7.  Humphry.    "On  the  Growth  of  the  Jaws,"  Phil.  Trans.,  1871. 

8.  Julin.    "Recherches  sur  I'Ossification  du  Maxillaire  inferieur,  "  Archives  du  Biologic,  1880. 

9.  A.  Kerckring.    "  Osteogenia  Fcetuum,  "  1670. 

10.  Low.  "The  Development  of  the  Lower  Jaw  in  Man,"  Proc.  Anat.  Soc.  of  Great  Britain  and 
Ireland,  1905;  also  Proc.  Anatom.  and  Anthropolog,  Soc.  University  of  Aberdeen,  1906. 

11.  Magitot  et  Robin.  "  Memoire  sur  un  organe  transitoire  de  la  vie  foetale  designe  sous  le  nom 
de  cartilage  de  Meckel,"  Annales  des  Sciences  Naturelles  Zoologiques,  1862. 

12.  Masquelin.  "Recherches  sur  le  developpement  du  maxillaire  inferieur  de  I'homme,  "  Bulletin 
de  I'Acad.  Roy.  de  Belgique,  1878. 

13.  Mies.  "Ueber  die  Knochelchen  in  der  Symphyse  des  Unterkiefers  vom  neugebornen 
Menschen,"  Anat.  Anzeig.,  1893. 

14.  Meckel.     "  Handbuch  der  menschlichen  Anatomic,  "  1820. 

15.  Parker.    "On  the  Structure  and  Development  of  the  Skull  in  the  Pig, "  1874. 

16.  Rambaud  et  Renault.    "Origine  et  developpement  des  Os,"  1864. 

17.  Schafer.    In  Qmcin's  "  Elements  of  Anatomy,"  l(jO?i. 

18.  Schaffer.  "Die  Verknocherung  des  Unterkiefers  und  die  Metaplasifrage,  "  Archiv  fiir  mikro- 
skop.   Anatomie,    1888. 

19.  Spix.     "Cephalogenesis,  "  1815. 

20.  StrelzofE.  "Ueber  die  Histogenese  der  Knochen,"  Untersuchungen  aus  dem  path.  Instit.  zu 
Zurich,  1873. 

21.  Testut.    "Traite  d' Anatomie  Humaine, "  1899. 

22.  Thane.    In  Quain's  "Elements  of  Anatomy,"  1899. 

23.  Toldt.    "Prager  Zeitschrift  f.  Heilkunde,"  1884. 

24.  Wolff.    "Ueber  das  Wachsthum  des  Xintevldei&rs,"  Arch,  fiir  path.  Anat.  und  Physiologic,  1888. 


CHAPTER    XIV 
THE   DYNAMICS   OF   ERUPTION 

Introductory.  —  Certain  Facts.  —  The  Radicular  Elongation  Theory.  —  Interstitial  Growth  of 
Bone. — Deposition  of  Bone. — Blood  Pressure. — The  Epithelial  Theory. — The  Gubernaculum. 
— The  Influence  of  Nutrition. — The  Dates  of  Eruption. 

Introductory. — The  process  of  the  eruption  of  the  teeth  is  a  physio- 
logical mystery,  as  is  that  of  growth  generally.  Many  theories  have 
been  formulated  to  attempt  a  solution,  but  none  are  entirely  satis- 
factory. The  application  of  a  substantial  hypothesis  must  extend 
to  both  deciduous  and  permanent  dentitions;  to  teeth  which  appear 
at  a  later  or  earlier  period  than  when  they  are  expected — the  process 
of  apparition,  retarded  by  some  obscure  or  obvious  circumstances, 
as  in  cretins,  or  expedited  by  general  disturbances  of  growth,  as  by 
syphilis;  to  teeth  which  erupt  in  anomalous  positions;  and  to  teeth 
which,  though  fully  developed,  do  not  erupt  at  all.  In  considering 
this  rudimentary  question,  it  will  be  advisable  to  study  certain  ascer- 
tained facts,  to  narrate  various  theories,  and  to  draw  conclusions. 

Too  much  attention  has  been  given  to,  and  importance  placed  upon, 
the  examination  of  the  naked-eye  appearances  of  developing  teeth. 
The  dynamics  of  eruption  are  concerned,  not  only  with  the  nature 
of  the  body  which  moves,  but  with  the  cause  of'^the  motion  which 
impels  it  to  the  surface,  and  they  begin  to  work  long  before  any  appre- 
ciable alteration  could  become  visible  to  the  unaided  eye.  Histology 
will  help,  however,  in  the  elucidation  of  the  matter,  and  also  the 
histogenesis  of  the  teeth  and  jaws  of  the  higher  mammals,  such  as  the 
Carnivora  and  the  Primates.  The  deductions  made  from  a  considera- 
tion of  the  emergence  of  the  teeth  from  the  gum  in  the  mouths  of 
fishes  are  wholly  indefensible,  especially  when  one  of  the  lowest  types 
of  fish — the  Chondropterygii — is  employed. 

Certain  Facts. — The  deciduous  tooth  germs  are,  from  the  com- 
mencement of  their  formation,  so  placed  that  they  almost  invariably 


PLATE   V 


The  Mandible  of  an  Adult.     X  ^ 


CERTAIN  FACTS  287 

bear  a  direct  relationship  to  the  developing  bone  of  the  jaw.  In  coronal 
sections  through  the  head  of  a  human  embryo  of  12  cm.  length,  four 
areas  of  ossification  appear.  These  occupy  the  site  of  the  future  alveolar 
processes.  These  osseous  areas,  as  observed  in  such  a  section,  are 
bifurcated  outwardly,  /'.  e.,  on  the  oral  side,  and  towards  the  middle 
of  the  branching  the  tooth  germs  are  directed.  In  both  maxilla  and 
mandible  they  are  turned  towards  the  middle  line.  The  amount  of 
bone  formed,  say  at  the  fiftieth  day  of  intra-uterine  life,  is  already 
considerable;  that  of  the  tooth  germ  only  small;  the  two  are  quite 
disproportionate.  The  rate  of  development  between  them  is  also 
unequal. 

By  about  the  hundred  and  twentieth  day  a  definite  bony  cup  has 
been  produced,  which  gives  lodgement  to  the  still  rapidly  growing, 
but  very  incomplete  tooth  germ;  and  shortly  afterwards,  perhaps 
twenty  or  thirty  days,  this  cup  is  a  deep  wide-mouthed  gutter  of  bone. 
The  free  margins  of  the  cups  subsequently  become  narrower,  and  at 
the  ninth  month  (birth)  each  tooth  germ  is  imbedded  in  a  closed  bony 
sac.  Absorption  of  the  crypts  placed  in  the  anterior  portions  of  the 
maxillae  and  mandible,  begins  to  take  place  in  Man  about  the  seventh 
month  before  birth.  It  proceeds  on  ordinary  physiological  lines  at 
the  expense  of  the  superior  and  anterior  surfaces.  This  absorption 
is  followed,  when  the  crown  has  emerged  through  the  orifice  of  bone 
and  gum,  by  a  rapid  development  of  bone  above  the  neck  of  the 
tooth.  This  bony  growth  keeps  pace,  pari  passu,  with  the  elongation 
of  the  roots,  and  the  increasing  depth  of  the  jaw  with  the  eruption  of 
the  teeth. 

Eruption  is  probably  a  continuous  process,  though  some  believe 
it  to  be  interrupted  by  periods  of  repose. i"  It  has  not  been  explained 
why,  when  once  the  forces  have  begun  to  act,  they  should  suddenh- 
suspend  their  operations  for  a  varying  period  of  time. 

Prior  to  their  being  shed,  the  deciduous  teeth  become  slightly 
separated  from  each  other.  This  is  accounted  for  by  the  growth  of 
the  bones  which  has  taken  place  since  they  were  erupted.  They  now 
occupy  a  more  prominent  position,  due  to  the  increase  in  the  dimen- 
sions of  the  crypts  behind,  which  are  beginning  to  accommodate  the 
larger  tooth  germs  of  the  permanent  dentition. 


288  THE  DYNAMICS  OF  ERUPTION 

The  sockets,  as  Mr.  Tomes"  insists,  grow  up  with  and  are  "moulded 
around  the  teeth  as  the  latter  elongate."  "The  socket  is  subservient 
to  the  position  of  the  tooth,  and  wherever  the  tooth  may  chance  to 
get  to,  there  the  socket  will  be  built  around  it." 

Eruption  appears  to  be  subject  to  the  three  general  laws  as  defined 
by  Debierre  and  Pravaz.'' 

1.  Teeth  of  the  same  denomination  appear  in  pairs; 

2.  From  the  point  of  view  of  time,  those  of  the  lower  precede  those 
of  the  upper  jaw; 

3.  The  first  deciduous  incisors  precede  the  second,  the  latter  the 
first  molars,  after  which  come  the  second  molars  or  perhaps  the  canines. 

It  is  a  well-known  clinical  fact  that  rickets  retards  and  syphilis 
accelerates  dental  eruption;  but  as  for  the  reasons,  there  are  no  evi- 
dences yet  forthcoming.  It  is  noteworthy  that  both  these  diseases 
produce  lesions  which  very  largely  affect  the  skeletal  tissues,  particu- 
larly the  former,  and  the  retardation  or  acceleration  in  eruption  may 
be  dependent  upon  the  influence  they  have  in  the  rate  of  growth  of 
the  bony  sockets  of  the  teeth. 

At  all  events,  it  would  seem  evident  that  a  direct  relationship  exists 
between  the  growth  of  bone  and  the  eruption  and  growth  of  the  teeth 
— a  relationship  which  has  a  physiological  as  well  as  a  pathological 
side.     The  hypothetical  aspect  is  quickly  becoming  the  actual  one.* 

*  A  case  which  may,  perhaps,  throw  some  light  on  this  obscure  subject  has  recently  been  described 
by  Mr.  A.  T.  Pitts,  in  which  there  was  a  remarkable  partial  failure  in  the  eruption  of  the  molars, 
associated  with  an  arrest  of  the  growth  of  the  mandible.  It  occurred  in  a  man,  aged  twenty-three 
years,  who  was  well  developed  except  with  regard  to  the  lower  jaw.  The  only  teeth  in  occlusion 
were  all  the  incisors  and  canines,  and  on  the  right  side,  the  first  upper  and  both  lower  premolars. 
On  the  left  side  the  mandibular  second  premolar  and  the  first  and  second  molars  were  present,  their 
crowns  being  only  just  exposed,  and  directed  considerably  inwards.  Above,  a  bridge  extended  from 
the  first  premolar  to  the  first  molar,  which  thus  rendered  it  impossible  to  determine  the  amount  of 
eruption  of  these  teeth.  The  second  molar  was  normally  erupted.  In  occlusion,  a  space  of  10  mm. 
intervened  at  the  widest  part.  The  first  right  mandibular  molar  was  incompletely  erupted.  In  the 
right  maxilla  the  premolar  and  first  molar  were  normal,  while  the  second  molar  was  only  just 
erupting.  The  patient  stated  that  the  condition  had  remained  stationary  for  some  years.  Radio- 
graphs revealed  the  fact  that  there  was  no  diminution  in  the  number  of  the  teeth,  the  complementary 
teeth  with  fuUy  formed  roots  being  still  unerupted..  including  a  small,  irregular  calcified  mass  behind 
the  second  upper  premolar.  The  anteiior  portion  of  the  mandible  in  the  incisor  region  was  fully 
developed,  but  the  posterior  parts  not  so.  Here  the  compact  bone  was  greatly  reduced  in  depth: 
the  mandibular  canal  appeared  to  be  in  direct  contact  with  the  lower  border  of  the  jaw,  and  no  bone 
intervened  between  the  apices  of  the  roots  of  the  lower  molars  and  the  compact  bone.  The  most 
superficial  portions  of  the  alveolar  processes  seemed  to  be  somewhat  denser  than  usual .     (See  Fig.  296.) 


CERTAIN  FACTS 


289 


The  governance   of   the   growth   of   the   body — including   the  osseous 
system — would  seem  to  lie  in  a  hitherto  insignificant  and  unsuspected 


Fjg.  -^93 

■T 

^ 

Plaster  cast  of  the  teeth  of  a  patient  affected  by  aci'onir.i;;!! 
method  of  their  occlusion. 

Fig.  29.1 


Fig.  294. — Head  of  an  a. hill,  aged  twenty-two  years,  affected  with  acromegaly.  The  face  has 
become  greatly  elongated  and  enlarged,  due  chiefly  to  the  increase  in  size  of  the  maxilte  and 
mandible,  especially  the  latter.  The  nostrils  are  large  and  broad,  the  eyelids  thickened,  the  ears 
enormously  hypertrophied.     Bitemporal  hemianopia  is  present. 

Fig.  295. — The  same  as  preceding  Fig. — side  view. 

quarter,   and   evidence  seems  to  be  accumulating  to  show  that  the 
pituitary  body,  which  weighs  only  from  5  to  10  grains,"  situated  near 

19 


290  THE  DYNAMICS  OF  ERUPTION 

the  anterior  part  of  the  midhne  of  the  base  of  the  brain,  in  some,  as 
yet  abstruse  fashion,  presides  over  the  function  of  growth. 

Fig.  296 


Radiograph  showing  incomplete  eruption  of  the  mandibular  molars.      Cf.  Fig.  240. 

Keith'''  has  described  certain  changes  occurring  in  the  jaws  of  Man 
when  associated  with  acromegaly.  He  says:  "During  the  eruption 
of  the  teeth  the  growth  of  the  upper  and  lower  maxilla  is  so  coordi- 
nated that  the  upper  and  lower  teeth  fall  into  correct  apposition. 
There  are,  at  least,  two  factors  concerned  in  this  coordination:     (i)  A 


THEORIES  291 

substance  evidently  derived  from  the  pituitary  body  which  acts  on  the 
osteoblasts  so  that  they  respond  readily  to  certain  stimuli,  and  (2) 
certain  forces  or  stimuli  which  act  directly  on  the  jaws.  These  stimuli 
arise  (a)  from  the  developing  teeth;  {fi)  from  pressure  applied  to  the 
alveoli  during  mastication;  (/-)  from  the  direct  reaction  of  the  muscles 
of  mastication.  The  last-named  force  acts  chiefly  on  the  lower  jaw." 
(Figs.  293  and  294.) 

It  would,  therefore,  appear  that  the  eruption  of  the  teeth  is  probably 
brought  about  indirectly  by  a  complex  physiological  process  which 
arises  in  and  is  governed  by  the  function  (?.  e.,  the  secretions)  of  the 
pituitary  body,  and  directly  by  the  actual  growth  of  the  bone  of  the 
jaws  which  is  destined  to  become  the  more  or  less  permanent  sockets 
of  the  teeth — a  physiological  process  as  yet  but  little  understood, 
whose  modus  operandi  cannot  be  reduced  to  a  mathematical  certainty, 
and  whose  operations  terminate  with  a  completion  of  the  growth  of  the 
alveolar  processes. 

It  seldom  happens  that  there  are  irregularities  in  the  order,  or  in 
the  position  of  the  deciduous  teeth — eruption  is  normal  from  that 
point  of  view. 

THEORIES 

A  brief  examination  of  the  theories  which  have  from  time  to  time 
been  advanced  must  now  be  made,  with  the  arguments  pro  and  con,  the 
most  fantastic  of  the  numerous  speculations  being  purposely  omitted. 

The  Radicular  Elongation  Theory. — This  is  the  simplest  as  defined 
by  Kolliker,'"  Lcvcque.^i  Robin  and  Magitot,^'  and  Tomes. ^'^  The 
last-named  authority  readily  admits  that  against  this  are  the  con- 
stantly recurring  facts  that  (i)  teeth  possessing  very  stunted  roots 
often  erupt;  (2)  that  the  structural  completion  of  the  whole  length 
of  the  roots  does  not  necessarily  prevent  a  tooth  from  remaining  im- 
bedded in  the  bone  throughout  the  life  of  an  individual;  and  (3)  that 
"when  a  healthy  normal  tooth  is  being  erupted,  the  distance  travelled 
by  its  crown  often  greatly  exceeds  the  amount  of  addition  to  its  length, 
which  has  gone  on  during  the  same  period."  This  last  fact  is  well 
observed  in  connexion  with  the  maxillary  canines,  as  also,  at  times, 
with  teeth  which  erupt  in  inverted  positions. 


292  .  THE  DYNAMICS  OF  ERUPTION 

Theory  of  "Bone  Currents." — An  interstitial  growth  of  bone  or 
so-called  "bone  currents"  was  proposed  by  Coleman,^  as  occasioning 
the  movements  of  the  developing  teeth.  These  "bone  currents" 
were  supposed  to  be  peculiar  to  the  jaws,  and  were  accompanied 
by  denudation  of  the  alveolar  margins,  bringing  at  length  the  teeth 
into  proper  position. 

Deposition  of  Bone  Theory. — Allied  to  this,  was  the  belief  that  a 
deposition  of  bone  at  the  base  of  the  dental  crypts,  and  also  that 
a  certain  amount  of  contraction  of  the  alveolar  plates  achieved  the 
same  object. 

Regarding  the  two  latter  theories  it  may  be  asked:  "Why  do 
these  forces  cease?"  or  conversely:  "Why  do  not  these  forces  pro- 
ceed until  the  occupants  are  completely  forced  out  of  their  alveolar 
sockets?"  There  is  no  contraction  of  the  alveolar  process  about  the 
roots  of  teeth  of  persistent  growth  such  as  the  incisors  of  rodents. 

Blood  Pressure  Theory. — That  the  blood  pressure  in  a  vascular 
tissue  which  lies  between  the  developing  tooth  and  its  surroundings 
is  a  mechanical  factor  is  a  theory  advocated  by  Mr.  Constant.*  He 
writes:  "Assuming  that  the  physiological  process  of  dentinification 
can  exercise  independent  mechanical  force,  and  is  a  factor  in  the 
causation  of  eruption,  it  must,  since  action  and  reaction  are  equal 
and  opposite,  divide  the  honours  with  the  blood  pressure  as  a  factor 
hitherto  quite  unrecognized."  "The  fact  that  teeth  with  fully  formed 
roots  remain  unerupted  can  be  more  easily  explained  by  this  theory 
than  by  any  other,  because  it  alone  can  account  for  the  space  obtained 
for  the  fully  developed  roots,  which  often  occupy  abnormal  positions. 
In  other  words,  the  blood  pressure,  acting  as  it  does  equally  in  all 
directions,  makes  room  for  the  developing  root  in  the  direction  of 
least  resistance.  Normally  this  is  in  the  direction  of  the  advancing 
crown,  but  occasionally  it  is  elsewhere." 

It  will  be  observed  that  in  Mr.  Constant's  description  of  his  con- 
ception of  this  force,  he  asserts  that  the  blood  pressure  "acts  equally 
in  all  directions."  If  this  is  so,  it  would  act  on  the  superior  surface 
of  the  crown  of  the  developing  teeth,  equally  as  on  the  lateral  and 
the  inferior  surfaces.  These  suggestions  seem  to  be  based  upon  the 
nature  of  the  "jelly-like"  consistence  of  the  tissue  in  which  the  teeth  are 


THEORIES  293 

imbedded.  There  is  no  gelatinous  tissue  found  in  this  region,  as  any 
properly  prepared  section  will  demonstrate.  Neither  is  it  "extremely 
vascular."  The  suggestion  almost,  if  not  entirely,  implies  a  condition 
of  hyperaemia  around  the  root  follicles.  The  relationships  of  the 
parts  which  appear  in  the  diagram  accompanying  his  paper  are 
non-existent,  the  immediate  peridental  environment  being  quite 
inaccurate  and  exaggerated. 

Again  it  is  obvious  that  microscopical  and  not  macroscopical  exami- 
nations are  required.  Further,  if  this  theory  was  acceptable  the  blood 
pressure — unless  it  was  itself  stopped — would  slowly  but  surely  cause 
entire  extrusion  of  the  teeth. 

"Epithelial"  Theory. — The  "epithelial"  theory,  ably  advocated  by 
Mr.  Warwick  James,"  has  arisen  in  connexion  with  certain  persistent 
epithelial  remains  of  the  tooth  band  and  enamel  organ,  found  in  rela- 
tively small  quantities  in  the  jaws  over  the  crowns  of  erupting  decid- 
uous teeth.  Their  remains,  according  to  this  observer,  form  three 
principal  groups — superficial,  intermediary,  and  deep — near  the  external 
surface  of  the  enamel  organ,  and  are  "the  determining  factor  in  direct- 
ing the  tooth  to  its  fixed  position  in  the  jaw."  He  finds  that  the 
epithelium  is  produced  continuously  up  to  the  period  of  eruption, 
and  that  there  is  probably  a  continuity  of  epithelial  tissue  extending 
between  the  surface  epithelium  and  the  remains  of  the  enamel  organ. 
"A  zone  of  rarefaction  exists  over  the  teeth  in  the  stages  of  eruption." 
' '  The  path  of  eruption  is  prepared  by  the  degeneration  of  the  epithelium ; 
the  tissues  which  are  apparently  very  dense,  become  loosened  and 
rarefied  by  the  ramifications  of  the  epithelium,  and  particularly  by 
the  changes  in  the  zone  of  rarefaction."  The  so-called  "glands"  of 
Serres  degenerate  and  diminish  the  depth  of  tissue  over  the  crowns 
of  the  erupting  teeth. 

While  accounting  for  the  conditions  which  probably  expedite  the 
passage  of  the  teeth  from  their  crypts,  through  the  gum,  nothing  here 
is  said  as  to  the  force  of  initiation,  or  how  the  teeth  begin  to  move. 
Moreover,  the  deciduous  series  apparently  only  are  considered.  The 
histological  differences  existing  in  the  region  around  the  developing 
permanent   teeth    must   be   reckoned    with,    and    in    this   respect   the 


294  THE  DYNAMICS  OF  ERUPTION 

"epithelial  theory"  fails,  nor  can  it  be  applied  to  the  eruption  of  ovarian 
teeth. 

It  may,  however,  be  asserted  that  in  these  views  an  advance  has 
been  made,  particularly  in  the  knowledge  as  to  the  dates  of  the  erup- 
tion of  the  deciduous  teeth. 

Gubernaculum  Theory. — ^A  revival  of  the  gubernaculum  theory 
has  recently  occurred.  Mr.  Thornton  Carter^  writes:  "I  am  of  the 
opinion  expressed  by  the  'older  anatomists'  that  the  gubernaculum 
is  concerned  in  some  way  in  directing  or  effecting  the  eruption  of  the 
teeth."  "I  believe  the  most  important  factor,  and  the  only  one  which 
provides  a  satisfactory  working  hypothesis  for  the  practitioner  in 
dealing  with  cases  of  irregularity  of  the  teeth,  to  be  the  force  exercised 
on  the  tooth  through  the  gubernaculum."  In  a  later  article  he  recedes 
from  this  position,  however,  and  becomes  more  guarded,  for  after 
dealing  with  the  question  from  the  point  of  view  of  the  cartilaginous 
fishes,  in  which  "the  mechanism  of  eruption  is  constantly  in  opera- 
tion unobscured,"  he  concludes  that  "in  Man  the  cause  of  eruption, 
or  at  least  an  active  factor  in  producing  eruption,  is  to  be  found  in  the 
disproportionate  growth  occurring  in  the  tissues  forming  the  tooth 
and  the  tissues  surrounding  the  tooth." 

Strong  objection  may  with  reason  be  taken  to  this  theory,  for  the 
operations  in  the  group  of  fishes — particularly  the  lowest  type  of  fish 
— are  so  dissimilar  to  those  of  the  higher  mammals,  that  comparisons 
and  deductions  are  superfluous,  and  offer  an  interesting  example  of 
paralogism.  The  Chondropterygyii  and  the  Primates  cannot  be  thus 
approximated — they  are  far  too  widely  separated  in  the  scheme  of 
Nature. 

"Epiblastic"  Theory. — It  is  hardly  necessary  to  mention  that  some 
have  considered  that  enamel,  being  epiblastic  in  origin,  should,  like 
other  dermal  tissues,  have  an  inherent  tendency  to  "come  to  the 
surface."  The  absurdity  of  this  tenet  is  at  once  apparent,  for  the 
teeth  of  some  of  the  Edentata  which  possess  no  enamel,  erupt — while 
occasionally  odontomes  composed  entirely  of  dentine  or  cementum 
also  seem  to  undergo  the  same  process. 

Addition  of  Dentine. — The  addition  of  dentine  to  the  extremities  of 
the  roots  has  been  referred  to  by  Norman  Broomell.^     He  too  realizes 


THE  TIMES  OF  ERUPTION  295 

the  difficulties  of  explanation,  for  he  writes:  "In  a  general  way  the 
advancement  of  the  crown  may  be  said  to  result  from  the  elongation 
of  the  root  by  the  addition  of  dentine  to  its  free  extremity.  But  when 
it  is  taken  into  consideration  that  the  cuspid  teeth,  both  deciduous  and 
permanent,  have  their  roots  fully  or  nearly  calcified  before  they  begin 
to  advance  towards  the  surface,  an  exception  to  the  generally  accepted 
theory  is  established." 

Influence  of  Nutrition. — The  influence  of  nutrition  is  believed  by 
Sayre  Marshall'-  to  have  some  efifect  upon  the  erupting  crowns.  Some 
change  occurs  in  the  gums  and  in  the  walls  of  the  dental  crypts.  There 
is  possibly  a  withdrawal  of  a  certain  amount  of  the  blood  supply  of 
the  neighbouring  parts  through  great  activity  in  the  growth  of  the 
dental  follicle  "just  preceding  and  during  the  period  covered  by  the 
process  of  the  extension  of  the  crown.  This  is  one  aspect  of  the  belief 
in  the  physiological  processes  of  gi'owth  which  appears  to  the  author 
to  be  the  only  tenable  theory  at  present  worthy  of  acceptance." 

THE    TIMES    OF    ERUPTION 

There  is  a  great  divergency  of  opinion  regarding  the  dates  of  eruption 
both  of  the  deciduous  and  of  the  permanent  dentition.  The  reasons 
are  quite  obvious;  systematic  attempts  have  been  rarely  conducted, 
and  published  tables  have  been  copied  from  text-book  to  text-book. 

An  admirable  example  of  the  method  of  deduction  en  circle  may  be 
mentioned  in  the  fact  that  some  writers  have  given  statistical  informa- 
tion of  eruptive  dates  from  the  examination  of  collections  of  crania 
in  Anatomical  Museums.  The  rate  of  progress  or  stage  of  the  phe- 
nomena is  noted  in  skulls  of  certain  age;  therefore,  that  represents 
the  conditions  at  that  stage. 

It  may  be  easily  forgotten,  however,  that  the  age  of  the  skulls  has 
been  probably  empirically  founded  upon  the  state  of  eruption.  The 
age  of  the  skulls  themselves  is  guessed  by  the  amount  of  growth  of 
the  teeth,  and  the  phases  of  eruption,  and  the  dates  of  eruption  are 
governed  by  the  supposed  age  of  the  skulls.  ^Another  fallacy  also 
exists,  and  that  is,  probably,  a  large  proportion  of  these  crania  which 
find  their  way  into  Museums  are  from  diseased  persons — rickety  and 


296 


THE  DYNAMICS  OF  ERUPTION 


syphilitic;  and  hence,  from  the  point  of  view  of  time,  are  perfectly 
unreliable. 

The  real  truth  cannot  be  attained  until  a  body  of  dental  surgeons 
who  are  parents,  and  who  are  willing  carefully  to  note  the  actual 
dates  of  the  observed  eruption  of  the  various  teeth  in  the  mouths  of 
their  children,  will  determine  to  collect  statistics  in  this  important 
matter. 

Meanwhile  a  step  in  the  proper  direction  has  been  made,  as  already 
mentioned,  by  Mr.  Warwick  James,"  who  has  recently  published  a 
list  of  approximate  dates  of  the  eruption  of  the  permanent  teeth  of 
4850  children  below  the  age  of  twelve  years.  They  were  certainly 
attending  as  patients  at  a  Children's  Hospital,  but  it  is  probable  that 
these  computations  are  those  of  children  free  from  any  disease  which 
would  affect  the  growth  and  eruption  of  their  teeth. 

The  following  list  comprehensively  shows  at  a  glance  the  table  of 
dates  given  by  several  eminent  anatomists  and  observers. 


Order  of  the  eruption  of  the  teeth. 


Dates  of  eruption. 


A 
Deciduous  Dentition. 
First  mandibular  incisor 
First  maxillary  incisor    . 
Second  mandibular  incisor 
Second  maxillary  incisor 
First  mandibular  molar  . 
First  maxillary  molar 
Second  mandibular  molar 
Second  maxillary  molar  . 
Mandibular  canine    . 
Maxillary  canine  ... 

B 

Permanent  Dentition. 
First  mandibular  molar  . 
First  maxillary  molar 
First  mandibular  incisor . 
First  maxillary  incisor     . 
Second  mandibular  incisor 
Second  maxillary  incisor 
First  mandibular  premolar 
First  maxillary  premolar 
Second  mandibular  premolar"!  ^^^j^    ^^^ 
Second  maxillary  premolar  . ./  " 

Mandibular  canine    .  .  ;lilth  to  12th 


1 7  th  to  9th 
/    month 
[Some  months 

after 

4  or  5  months 

later 

^About  24th 
month 


>6th  year 
Wth  year 
Isth  year 
>9th  year 


|6th  to  8th  month: 
isth  to  1 2th  mth.l 

1 1 2th  to  i6th  mth. 


20th  to  30th  mth. 
15th  to  20th  mth. 

6th  to  7th  year 
7th  to  8th  year 
8  th  to  9th  year 
9th  to  nth  year 


Debierre  and  Pravaz. 


7th  month 
loth  month 
l6th  month 
20th  month 
24th  month 
26th  month 
28th  month 
30th  month 

>30thto33dmonth|  [•24th  month 


7th  to  8th  month 
loth  month 
i2th  to  14th  month 
15  th  month 
15th  to  1 8th  month 
1 8th  to  20th  month 

>4th  month 


5th  to  6th  year 

5  th  to  6th  year 

7th  year 

7th  year 

1 8  th  year  and 

/     6th  month 

9th  to  1 2th  year 


>iith  to  13th  year'  /iith  year 


Maxillary  canine 
Second  molars 
Third  molars  . 


year 


>iith  to  13th  year:} nth  to  12th  year 


Yr.  Mth. 
6   6 


I2th  to  13th year  13th  to  15th  year  \  I2tli  to  13th  year   |il 

17th  to25th  year  17th  to  40th  year  |  19th  to  25th  year 


REFERENCES  297 


References 

1.  Broomell.    "Anatomy  and  Histology  of  the  Mouth  and  Teeth,"  1912. 

2.  Carter.  "The  Mechanism  of  the  Eruption  of  the  Teeth,"  British  Denial  Journal,  1904,  also 
1910. 

3.  Coleman.     Si.  Bartholomew's  Hospital  Reports,  vol.  xii,  18^6. 

4.  Constant.  "The  Mechanical  Factor  in  the  Eruption  of  the  Teeth,  "  The  Journal  of  the  British 
Dental  Association,  1896. 

5.  Debierre  and  Pravaz.  "Contribution  a  I'odontog^nie  des  Mammiferes, "  Archives  de  Physio- 
logie,  1886. 

6.  Dieulafe  and  Herpin.    "  Anatomie  de  la  Bouche  et  des  Dents, "  1909. 

7.  Gray.    "Anatomy,  Descriptive  and  Surgical,"  1907. 

8.  James  Warwick.  "A  Preliminary  Note  on  the  Eruption  of  the  Teeth,"  Proc.  Roy.  Soc.  of 
Med.,  June,  1909;  (with  Mr.  Pitts),  "Some  Notes  on  the  Dates  of  Eruption  in  Four  Thousand 
Eight  Hundred  and  Fifty  Children,  Aged  under  Twelve,"  Proc.  Roy.  Soc.  of  Med.,  1912. 

9.  Keith.  "An  Inquiry  into  the  Nature  of  the  Skeletal  Changes  in  Acromegaly,"  The  Lancet, 
April  15,  191 1. 

10.  KoUiker.    "  Die  Entwickelung  der  Zahnsackchen  der  Wiederkauer,  "  1863. 

11.  L^veque.  "  De  I'^ruption  des  dents,  au  point  de  vue  de  sa  mecanisme  et  des  accidents  qu'elle 
occasionne,  1 881. 

12.  Marshall,  Sayre.    "Principles  and  Practice  of  Operative  Dentistry,"  1909. 

13.  Robin  and  Magitot.    "  Recherches  sur  les  gouttieres  dentaires,  "  1889. 

14.  Tomes.     "A  Manual  of  Dental  Anatomy,"  1898. 

15.  Tomes.     "A  System  of  Dental  Surgery,"  1908. 

16.  Trousseau.     "Chnical  Lectures,"  vol.  iv. 

17.  Turner.     Trans.  Odonto.  Soc.  of  Great  Britain,  1901. 


CHAPTER    XV 
THE   FUNCTIONS   OF   THE   DENTAL   TISSUES 

Introductory. — The  Uses  of  Nasmyth's  Membrane. — Of  the  Enamel. —  Of  the  Dentine. — Of  the 
Dental  Palp. — Of  the  Periodontal  Membrane  and  Cementum. — Of  the  Gum. — The  Sensitive- 
ness of  Teeth. — Of  the  Enamel. — Of  the  Dentine. — Of  the  Cementum. — Dental  Pain. — Modifi- 
cations of  Sensation. 

Introductory. — A  tooth — and  by  this  is  implied  a  human  tooth — con- 
sists of  three  calcified  tissues — enamel,  dentine,  and  cementum — all 
extremely  hard  in  character,  but  each  essentially  different,  chemically, 
physically,  physiologically  (functionally),  and  histologically.  It  might 
have  been  supposed  that  Nature  in  order  to  supply  the  needs  of  speech, 
mastication,  and  adornment  would  have  provided  bodies  similar  in 
many  respects;  would  have  manufactured  a  tooth  of  one  material  only, 
and  paid  no  attention  to  minute  details  in  the  way  she  has  done.  For 
not  only  is  a  tooth  functional  as  a  whole,  but  every  portion  of  it  has 
its  uses,  and  when  abused  or  disused,  suffers  directly,  and  produces 
indirectly  diseases  or  defects  in  the  dental  organism. 

This  chapter  seeks  to  give  an  account  of  the  uses  of  these  various 
parts,  and,  taking  into  consideration  the  teeth  of  fishes,  reptiles,  and 
the  lower  animals,  to  prove  that  in  a  human  tooth  there  is  the  highest 
embodiment  of  all  the  functions  which  the  dental  organs  are  called 
upon  to  perform.  One  need  not  here  discuss  the  physiological  values 
of  the  various  dentitions  amongst  the  Vertebrates.  Attention  may, 
however,  be  given  to  a  description  of  the  particulars  of  the  several 
offices  of  the  hard  and  soft  parts  of  teeth,  taking  as  a  type  the  teeth 
of  Man. 

THE  USES   OF  THE  DENTAL  TISSUES 

Nasmyth's  Membrane. — The  precise  role  that  Nasmyth's  mem- 
brane plays  with  regard  to  the  enamel  is  at  present  but  little  under- 


THE   USES  OF   THE  DENTAL   TISSUES  299 

Stood.  Professor  Paul/  in  1894,  published  an  article  which  described 
the  real  nature  of  the  membrane,  and  there  hinted  that  its  function 
was  probably  a  protective  one.  He  says:  "It  seems  reasonable  to 
suppose  that  enamel  devoid  of  its  protection  could  hardly  compete 
with  that  which  is  shielded  by  it,"  and  asks:  "May  it  not  protect 
the  enamel  from  those  chemical  changes  constantly  at  work  in  the 
mouth?" 

A  study  of  the  histology  and  physiology  of  Nasmyth's  membrane 
has  been  much  neglected.  Writers  on  dental  caries  give  careful 
patho-histological  descriptions  of  the  enamel  and  the  dentine,  but 
some  have  invariably  ignored  the  presence  of  the  enamel  cuticle,  and 
it  is  just  possible  that  the  bacterial  plaques  of  Black  and  Miller  may 
be  merely  remnants  of  this  acid-resisting  tissue.  Whether  it  exists 
or  not,  and  if  so,  what  are  its  functions  in  the  teeth  of  certain  ungiilata, 
where  enamel  is  covered  partially  or  completely  b^'  cementum,  are, 
as  yet,  undecided  points.  The  writer  has,  in  nearly  every  human  tooth 
which  he  has  decalcified — in  carious  as  well  as  sound  normal  examples, 
even  in  teeth  of  patients  over  seventy  years  of  age — found  strips  of 
the  membrane  which  have  clung  most  pertinaciously  to  the  free 
surface  of  the  enamel.  He  is,  therefore,  inclined  to  place  great- 
importance  on  the  presence  of  the  tissue.  Its  position  on  the  circum- 
ference of  the  exposed  portions  of  the  teeth,  its  keratinous  character, 
its  resistance  to  acids  and  alkaline  solutions,  its  comparative  tough- 
ness, all  intrinsically  act  as  a  defence  to  the  underlying  parts.  If  it 
were  possible  that  mechanical  abrasion  or  attrition  could  have  no 
effect  upon  any  portion  of  it — these  two  forces  are,  of  course,  absent 
in  the  region  of  natural  pits  and  fissures — dental  caries  would  be  a 
thing  unheard  of  and  dental  disease  its  offspring  unknown.  The 
weakness  of  Nasmyth's  membrane  unfortunately  lies  in  its  extreme 
tenuity  and  inability  to  withstand  the  shocks  of  friction  or  traumatism, 
with  the  result  that  its  presence  may  possibly  really  act  as  a  menace 
when  torn,  microorganisms  finding  a  nidus  for  development  at  its 
ragged  margins. 

The  Enamel. — It  is  patent  to  every  reader  that  the  main  office  of 
enamel  is  to  form  a  hardened  case  for  the  body  of  the  tooth  proper, 
as   an   instrument  for   dividing,    comminuting,    and    triturating   food. 


300  THE  FUNCTIONS  OF  THE  DENTAL  TISSUES 

and  as  a  mechanical  protector  to  the  adjacent  dentine.  One  would 
expect  that,  for  these  properties,  the  patterns  of  all  animals  would  be 
universally  similar.  All  that  could  possibly  be  needed  would  be  a 
calcified  substance,  dense,  strong,  enduring,  non-frangible,  which 
would  act  like  a  chisel,  or  a  mill,  or  a  grindstone.  On  second  thoughts, 
however,  it  is  recalled  that  the  diet  of  animals,  fishes,  and  reptiles 
is  enormously  diversified,  and  then  one  begins  to  remember  the  mani- 
fold types  of  dentition,  such  as  the  carnivorous,  the  herbivorous,  the 
insectivorous,  the  omnivorous,  etc.  Here  is  found  an  explanation 
of  the  fact  that,  according  to  the  requirements  of  the  creature,  so 
has  Nature  modelled  the  jaws,  and  the  shapes,  sizes,  positions,  and 
numbers,  as  well  as  the  structure  of  the  teeth,  and  has  adaptively 
modified  even  the  enamel  for  the  varying  degrees  in  hardness  or  soft- 
ness of  the  food. 

But  the  beneficent  agencies  of  Nature  have  been  further  extended, 
and  a  beautiful  adaptation  of  means  to  an  end  is  seen  on  the  micro- 
scopical examination  of  various  enamels. 

In  Fishes  the  simplest  type  of  conformation  is  noticed.  A  plain, 
structureless,  minute  cap  of  enamel  serves  the  purpose  of  covering 
.the  dentine,  as,  exemplified,  Merlucius  vulgaris  (the  hake),  Aitguilla 
acutirostris  (the  eel). 

In  the  Mammalia,  on  the  other  hand,  the  most  complicated  patterns 
imaginable  are  found  amongst  the  rodents — the  squirrel,  the  beaver, 
etc. — where  the  arrangement  of  the  enamel  rods  is  wonderfully  appro- 
priate for  the  extreme  kind  of  work  which  the  teeth  have  to  under- 
take, in  the  gnawing  of  the  bark  of  trees,  the  cracking  of  the  shells 
of  nuts,  and  so  on.  Amongst  the  lower  animals  many  interesting 
and  suggestive  and  surprising  facts  come  to  light.  Thus,  the  Oryc- 
teropus  capensi  (the  Aard-vark  or  ant  bear),  of  the  Ethiopian  regions 
of  the  world,  has  no  enamel,  simply  because  its  food,  being  largely 
of  termites,  hard-crushing  organs  in  the  mouth  would  be  out  of  place. 

Again,  the  Manatiis  (sea-cow),  which  inhabits  the  coast  of  the  warm 
parts  of  the  Atlantic,  the  Bay  of  Bengal,  the  Australian  seas,  has 
eleven  pairs  of  cheek  teeth  in  maxillae  and  mandible,  subsists  on  sea- 
weeds and  aquatic  plants,  which  it  masticates  like  a  pig,  and  has  the 
enamel  rods  running  simply  in  straight  lines,  a  weak  sort  of  structure 


THE   USES  OF   THE  DEXTAL   TISSUES  301 

perfectly  adapted  to  the  tearing  part  of  the  leaves  and  stems  of  aquatic 
plants. 

The  Halicore  dugong  (dugong),  which  is  also  found  in  the  Red  Sea, 
off  the  coasts  of  India  and  Malay,  and  Australia,  being  entirely  marine, 
and  not  fluviatile  in  its  habits  like  the  Manatee,  eats  the  still  softer 
sea-weeds  of  these  waters,  and  does  not  even  require  an  enamel  casing 
to  its  cheek  teeth. 

Instances  need  not  be  multiplied.  Suffice  to  say  that  the  greater 
the  work  the  enamel  has  to  do,  the  more  complicated  the  pattern. 
So  in  the  molars  of  Man,  the  flexuous  courses  of  the  enamel  rods  give 
rise  to  a  very  complex  pattern,  showing  great  strength  and  rigidity; 
but  even  these  enamels  are  not  so  intricate  in  style  as  the  incisors  of 
the  porcupine  and  other  rodents,  while  they  are  more  so  than  the 
incisors  and  canines  of  Man. 

The  enamel  of  the  Marsupials  is  tubular.  The  real  reason  of  this 
tubularity  is  unknown.  It  probably  represents  an  imperfected  condi- 
tion, an  example  of  atavism. 

The  Dentine. — The  functions  of  dentine  are  not  difificult  to  define. 
To  give  substance  to  the  tooth  itself,  to  provide  a  centre  of  sensation, 
to  protect  the  pulp,  are  its  manifest  uses.  Enamel  is  without  the  pale 
of  nutrition,  the  pulp  is  highly  vitalized,  and  the  dentine  is  on  the 
borderland  of  the  living  and  the  dead — semi-vitalized,  if  one  may  so 
speak.  Nature  would  not  for  an  instant  tolerate  the  presence,  in  the 
midst  of  living  tissues,  of  a  dead  body  like  the  enamel.  The  result  is, 
therefore,  the  presence,  between  the  living  pulp  and  the  inert  enamel, 
of  a  large  area,  relatively  speaking,  of  a  tissue  which  is  marvellous 
and  unique. 

In  no  other  part  of  the  body  do  we  find  an  entirely  tubular  struc- 
ture like  dentine.  Its  peripheral  parts,  where  it  joins  the  inorganic 
enamel,  are  less  vitalized  than  its  central  parts.  This  explains  the 
reason  why  the  dentinal  tubules  are  not  of  the  same  calibre  through- 
out their  lengths.  The  contents  of  the  tubes  is  protoplasm,  which  is 
more  abundant  at  the  pulp  end  than  at  the  enamel  end.  Nature  would 
have  made  a  mistake  had  she  made  the  tubules  of  the  same  diameter 
throughout.  "In  width" — the  writer  quotes  from  his  "The  Histology 
and    Patho-histology   of    the    Teeth    and    xA.ssociated    Parts, "^    "they 


302  THE  FUNCTIONS  OF   THE  DENTAL   TISSUES 

vary  from  i.y.u  to  2.2 u  or  5,u  (Kolliker) ;  2.5/i  (Owen);  or  0.0055  rnm. 
.  The  diameter  of  the  tubes  diminishes  as  it  proceeds  outwards, 
till  at  the  peripheral  region  of  the  tooth  it  becomes  immeasurable." 

The  dentine  of  the  crowns  of  teeth  is  more  plentifully  supplied  with 
living  material  (protoplasm)  than  the  roots;  hence,  the  tubes  branch 
more  frequently  in  the  latter  than  in  the  former  situation.  The  writer 
believes  that  a  serous  exudation  fills  the  tubes,  bathing  the  dentinal 
fibrils — that  is,  the  peripheral  poles  of  the  odontoblasts — and,  accord- 
ing to  Howard  Mummery,  the  dentinal  nerves,  and  that  this  exudation 
is  nothing  more  nor  less  than  the  living  protoplasm  extruded  from  the 
trophic  pulp.  He  is  unable  at  present  to  offer  any  explanation  as  to 
the  utility  of  a  vascular  dentine  like  the  vaso-dentine  of  Merhicius, 
the  osteo-dentine  of  Esox  lucius,  and  the  folded  dentine  of  the 
Lepidosteus  or  Varanus  niloticus. 

The  Dental  Pulp. — Of  all  the  tissues  of  a  tooth  the  pulp  is  not  only 
the  most  sentient,  but  the  most  vitalized.  On  the  life  of  the  pulp 
depends  the  existence  and  welfare  of  the  tooth.  The  bloodvessels 
carry  to  and  remove  the  waste  products  of  the  life-giving  properties 
of  the  pulp;  the  nerves  serve  a  twofold  purpose,  a  sentient  one  to  act 
as  sentinels  in  case  of  danger,  and  to  act  also  as  regulators  of  the  blood 
traffic.  They  govern  the  blood  supply  very  largely,  and  through  their 
nutrient  influences  give  tone  to  the  arteries,  veins,  and  capillaries. 
As  a  whole,  the  pulp  affords  a  very  remarkable  physiological  resistance 
to  disease.  In  cases  of  pathological  absorption  of  cementum  and 
dentine  it  is  often  still  encased  by  an  area  of  dentine,  withstanding 
to  the  last  the  encroachments  of  the  morbid  conditions  which  produce 
the  rarefying  periostitis.  Then,  again,  in  cases  of  breach  of  surface 
of  enamel  or  dentine,  the  pulp  quickly  responds  by  depositing 
adventitious  or  secondary  dentine  on  its  surface  in  threatened  caries 
or  erosion  or  attrition. 

The  odontoblasts  probably  serve  three  distinct  functions:  (i) 
The  transmission  of  nervous  stimuli  to  the  pulp;  (2)  the  regulation 
of  the  intensity  of  the  stimuli;  and  (3)  a  trophic  control  over  the 
protoplasm  in  the  dental  tubes.  They  are  in  no  sense  nerves  them- 
selves. It  would  be  difiicult  to  believe  that  a  non-medullated  or  even 
a  medullated  nerve  fibre  could  exist  per  se  in  a  bony  tube  or  canal. 


THE   USES  OF   THE  DENTAL   TISSUES  303 

There  is  no  doubt  whatever  that  the  dentinal  fibrils  are  part  and 
parcel  of  the  odontoblasts,  and  it  is  highly  probable  that  the  latter 
act  as  sensation  transmitters,  intervening  between  the  terminal  arbori- 
zations of  the  sensory  pulp  nerves  on  the  one  side,  and  the  lifeless 
enamel  and  semi-vitalized  dentine  on  the  other.  They  do  not  form 
dentine  matrix.^ 

They  differ  in  size  in  different  parts  of  the  pulp;  they  are  not  con- 
cerned with  the  formation  of  pulp  nodules;  and  they  possess  a  more 
important  function  than  that  of  merely  keeping  the  dentinal  tubules 
patent.  The  main  argument  that  has  been  advanced  that  the  odonto- 
blasts cannot  be  associated  with  the  nervous  mechanism  of  the  teeth, 
on  account  of  their  embryological  factors,  would  appear  to  be  losing 
ground.  Derived  from  the  mesoblast  of  the  dentinal  papilla,  and  not 
from  the  epiblast  it  has  been  repeatedly  argued  that,  therefore,  they 
cannot  play  the  role  of  sensation  transmitters  to  the  dentine,  or  be 
at  all  analogous  or  homologous  with  the  nerve  ganglia  or  end  organs 
of  the  general  peripheral  nervous  system.  But  botanists,  zoologists, 
and  biologists  are  beginning  to  discover  fallacies  in  the  "Gastrceia 
Theorie"  of  Haeckel,^  who  definitely  laid  down  the  axiom  that  the 
nervous  system  is  derived  from  cells  of  epiblastic  origin.  It  is  now 
found  that  all  strict  homologies  based  on  this  three-germ  layer  are 
very  doubtful.  The  three-germ  layers — Dermatogen,  Periblem,  and 
Plerome — of  the  botanists  are  now  practically  discarded,  although 
previously  held  to  as  rigidly  as  even  McBride  holds  to  the  three-animal 
layers.  Von  Klaatsch  has  stated  that  the  mesodermal  cells  which 
give  rise  to  bone  are  really  epiblastic  cells  which  have  wandered  deeply. 
The  evolution  of  the  clavicle  shows  the  possibility  of  an  original  epi- 
blastic origin.  That  there  is  really  no  hard  and  fast  separation  between 
epi-  and  hypoblast  is  evidenced  by  the  development  of  some  of  the 
sponges,  and  many  of  the  facts  of  regeneration.  The  interested  reader 
may  refer  to  "The  Nervous  System"  by  Barker,^  and  the  still  more 
recent  writing  of  Korschelt  and  K.  Heider.^  The  facts  that  they 
not  only  submit,  but  emphatically  insist  on,  are  indisputable  and 
absolutely  irreconcilable  with  the  requirements  of  the  old-fashioned 
germ  layer  theory. ^  Thus  they  have  incontrovertibly  proved  that 
in  the    invertebrate    moss-animals    {Polyzoa  or  Bryosoa    which    form 


304  THE  FUNCTIONS  OF   THE  DENTAL   TISSUES 

Sub-kingdom  VI,  intervening  between  the  starfishes  and  the  worms,  of 
the  animal  kingdom)  the  whole  of  the  aHmentary  tract  is  of  ectodermal 
origin,  in  the  Planarian  worms  the  nervous  system  and  the  pharynx 
are  mesodermal.  Among  the  Vertebrates  in  Class  VII  {Protochorda) 
containing  lower  forms  of  life  than  the  lamprey  and  hag  fish  are 
certain  small  very  lowly  organized  marine  animals,  the  sea  squirts  and 
lancelets.  Closely  related  to  Amphioxus  are  Botryllus,  Salps,  Pyrosoma, 
Doliolum  Tritonis  amongst  others.  Of  these  the  nervous  system  of  the 
first  is  ectodermal,  of  the  others  mesodermal.  The  sea  squirts  present 
a  nervous  system  which  emanates  from  the  endodermal  cells. 

These  observations  coming  from  such  authorities  should  donner  a 
penser  a  quelqu'tm:  the  present  day  critic  cannot  possibly  ignore  them. 

The  Periodontal  Membrane. — It  is  a  task  of  no  little  difiiculty  to 
ascertain  precisely  the  real  physiological  properties  of  the  periodontal 
membrane.  One  knows  so  little  of  its  structure;  it  is  veritably  a 
terra  incognita. 

Pending  further  and  fuller  information,  however,  it  may  be  said 
that  its  functions  are  physical,  sensory,  nutrient,  and  formative. 

A  (i)  It  acts  as  an  apparatus  for  diminishing  the  force  of  concussion 
with  an  opposing  body,  whether  it  be  dental  or  otherwise,  (ii)  It 
affords  a  fibrous  attachment  to  the  teeth,  Malassez,  in  1885,  comparing 
it  to  a  ligament.  (Hi)  It  provides  a  layer  of  soft  material  in  which 
bloodvessels  and  nerve  fasciculi  to  supply  the  teeth  may  ramify  with- 
out risk  of  damage  or  permanent  and  inoperable  injury  by  mechanical 
shock.  Through  its  venous  supply  it  becomes  (B)  sensory,  an  impor- 
tant function  in  that  it  is  capable  of  detecting  pain,  a  beneficial  arrange- 
ment on  the  part  of  Nature.  (C)  Like  the  periosteum  of  other  bones 
it  possesses  a  certain  degree  of  trophic  influence  on  the  alveolar  walls 
of  the  dental  sockets,  and  (D),  it  is  formative  in  that  it  is  capable  of 
very  frequently  providing,  by  virtue  of  its  osteoblasts,  fresh  tissue 
(hyperplasic  cementum)  on  its  inner  aspects,  which  is  an  evidence 
of  its  reaction  to  injurj-  of  a  traumatic,  chemical,  or  bacteriological 
character. 

The  Cementum. — As  far  as  cementum  is  concerned,  the  author 
believes  that  it,  too,  like  enamel,  is  devoid  of  life;  that  normally  the 
lacunae  with  their  containing  corpuscles  are  absent;  that  when  they 


THE   USES  OF  THE  DENTAL  TISSUES  305 

do  appear,  they  are  symptomatic  of  a  previous  inflammation  of  the 
periodontal  membrane,  or  some  form  of  irritation  of  that  tissue, 
which  induces  a  hyperplasia,  on  account  of  the  revived  activity  of  the 
osteoblasts  in  the  membrane.  The  inference,  therefore,  is  that  human 
cementum  serves  as  a  sort  of  dense,  non-sensitive,  inert  covering^  for 
the  dentine  of  the  roots  of  teeth,  being  analogous  to  and  homologous 
with  the  peripheric  lamellae  of  compact  bone.  The  proof  of  this 
statement  has  not  yet  been  worked  out,  but  the  writer  hopes  some  day 
to  put  on  record  his  observations  on  this  subject.  Meanwhile,  he 
entirely  disagrees  with  Tomes,"  who  says  "The  human  tooth  is  con- 
nected with  the  living  organism  very  intimately,  even  though  its 
special  tissues  are  extra-vascular.  For  blood  vessels  and  nerves  enter 
the  tooth  pulp  in  abundance;  the  dentine  is  organically  connected 
with  the  pulp  by  the  dentinal  fibrils;  these  are  connected  with  the 
soft  cement  corpuscles,  which  again  are  brought  by  their  processes 
into  intimate  relationship  with  similar  bodies  in  the  highly  vascular 
periosteum.  So  that,  between  pulp  inside  and  periosteum  outside 
there  is  a  continuous  chain  of  living  plasm." 

In  the  molars  of  the  horse,  and  some  ruminants,  it  serves  to  main- 
tain a  rough  uneven  surface  to  the  crowns,  for  the  purpose  of  the 
thorough  comminution  of  food;  and  in  the  elephant,  it  binds  together 
the  plates  of  enamel  and  dentine  which  form  the  component  parts  of 
the  molars. 

The  Gum. — On  account  of  its  smooth  surface  the  gum  acts  as  a  pro- 
tective covering  to  the  alveolar  processes  of  the  jaws,  to  the  periosteum 
of  which  it  is  also  nutritive  through  its  abundant  blood  supply.  It  fills 
up  the  triangular  interdental  spaces,  which  largely  prevents  the  lodge- 
ment of  food  in  these  situations.  By  means  of  its  mucous  glands  it 
probably  has  some  share  in  the  general  lubrication  of  the  mouth.  It 
furnishes. a  set  of  blood  vessels  to  the  periodontal  membrane.  In 
certain  Ungulata  it  provides  a  biting  pad  against  which  the  mandibular 
incisors  are  applied. 

From  what  has  been  said  it  is  clear  that,  even  in  elementary  subjects 
such  as  have  been  hurriedly  sketched  above,  there  is  much  yet  to 
learn ;  and  it  is  only  by  studying  Comparative  Anatomy,  by  examining 
the  histology'  and  embryology  of  parts,  and  by  correlating  the  ascer- 


306 


THE  FUNCTIONS  OF  THE  DENTAL  TISSUES 


tained  facts  and  theories  of  dental  pathology  and  clinical  experience 
with  them,  that  one  can  hope  to  arrive  at  satisfactory  and  scientific 
conclusions  which  would  be  of  permanent  value  to  the  dental  profession. 


THE    SENSITIVENESS    OF    TEETH 

Enamel. — The  sensitiveness  of  teeth  is  a  normal  physiological 
condition.  As  far  as  is  at  present  known,  enamel  itself  is  not  inner- 
vated. Its  physical  properties  are  such  as  to  prevent  it  from  generating 
sensations  of  any  kind.  There  are  no  nerve  endings  in  enamel.  Mor- 
genstern  and  Romer  believe  that  nerve  end  organs  can  be  found  in 

Fig.  298 


Diagram  of  a  reflex  act.  The  sensory  nerves 
in  (T")  the  tongue  and  (C)  cheek  send  stimuli 
to  (B)  the  brain,  which  transmits  them  to  (P) 
the  dental  pulp.  Thus  exceedingly  sweet  sub- 
stances on  the  tongue  will,  at  times,  produce 
odontalgia. 


Diagram  of  a  reflex  act.  An  electrical  im- 
pulse may  set  up  momentary  odontalgia  when 
two  dissimilar  metals,  such  as  those  of  the 
edge  of  a  hand  mirror  (M)  and  (F)  of  a  metallic 
filling,  meet,  and  the  circuit  is  completed  by 
(C)  the  mucous  membrane  of  the  cheek,  the 
saliva  acting  as  the  electrolyte. 

the  enamel  spindles  which  exist  at  the  amelo-dentinal  junction,  but 
are  variable  in  number,  shape,  and  size.  These  views,  however,  are 
not  generally  held,  and  indeed  there  are  many  insuperable  difificulties 
connected  with  the  theory — objections  of  histogenesis,  of  phylogeny, 
of  reason.  Enamel  perhaps  may  mechanically  transmit  impulses  to 
the  pulp  by  shock,  but  it  is  incapable  per  se  of  initiating  them. 


THE  SENSITIVENESS  OF  TEETH  307 

It  is  a  remarkable  fact  that  the  physiological  phenomena  set  up 
when  substances  of  various  kinds,  taken  into  the  mouth,  are  brought 
into  direct  contact  with  the  teeth  cannot  precisely  be  described.  This 
sensitiveness  is  extraordinary,  distinguishing,  accurately  and  imme- 
diately, between  the  shapes,  proportions,  and  constitutions  of  wholly 
dissimilar  foreign  bodies  such  as  shot  in  game,  a  crumb  of  bread,  a 
delicate  hair,  a  piece  of  thread — silk  or  otherwise — a  fragment  of  gritty 
sand,  or  particle  of  comminuted  food — a  sensitiveness  which  causes 
its  rejection  or  retention — a  sensitiveness,  too,  of  degree,  whereby 
dififerences  are  at  once  detected  between  the  comparative  softness  of  a 
small  leaden  bullet,  and  the  dense  hardness  of  a  piece  of  shell.  It  is 
extremely  probable  that  the  sensory  nerves  distributed  to  the  cheek 
and  the  tongue  materially  assist  the  perception  of  the  minute  tactile 
impressions  made  upon  the  enamel,  and  produce  a  complete  series  of 
sensations  at  present  entirely  inexplicable.  As  long  as  no  breach 
of  surface  occurs  this  sensation  is  one  of  touch  or  discomfort,  not 
one  of  pain. 

Dentine. — Certain  molecular  movements  occurring  externally  cause 
a  distinct  perception  or  group  of  perceptions  on  the  part  of  the  pulp, 
with  its  prolongations  in  the  dentinal  tubes,  which  converts  these 
movements  into  nerve  impulses,  that  immediately  pass  by  an  afferent 
channel  to  the  brain.  The  dentine,  and  through  it  the  pulp,  acts  like 
a  sense  organ:  when  exposed,  the  periodontal  membrane  acts,  too, 
like  a  sense  organ  in  a  dififerent  way,  and  is  of  a  different  character  to 
that  of  the  pulp.  Miiller's  law  of  specific  irritability  can  be  applied 
to  the  dentine  {i.  e.,  the  pulp)  just  as  well  as  to  the  optic  or  the  auditory 
nerve.  It  states  that  every  sensory  nerve  reacts  to  one  form  of  stim- 
ulus, and  gives  rise  to  one  form  of  sensation  only.  Thus  chemical, 
mechanical,  thermal,  electrical,*  and  other  sensigenous  impressions  pro- 
duce only  one  subjective  effect — pain.  Nor  does  the  intensity  of  this 
result  depend,  as  in  other  parts,  upon  the  strength  of  the  stimulus;  in 
the  tooth  this  proportionately  breaks  down,  and  Weber's  law  or  Fech- 
ner's — "The  increase  of  stimulus  which  is  required  to  produce  distinct 
increase  of  sensation  always  bears  the  same  ratio  to  the  whole  stimulus" 

*  See  Appendix — Note  C. 


308  THE  FUNCTIONS  OF  THE  DENTAL  TISSUES 

— fails,  even  though  the  stimulus  be  of  the  slightest.  Pain  is  not  merely 
an  exaggerated  tactile  or  temperature  sensation.  In  cases  where  a 
tactile  sense  is  deficient,  the  pain  sense  may  be  exalted.  It  is  well 
defined,  and  regulated  by  a  distinct  set  of  nerve  fibres.  The  dentine, 
like  the  cornea,  perceives  only  painful  impressions;  it  cannot  discrimi- 
nate between  tactile  or  thermal  sensations. 

Dentinal  sensibility,  to  repeat,  is  a  normal  physiological  condition. 
In  Man  it  reaches  its  highest  degree  of  development.  If  dentine  were 
not  sensitive,  frightful  havoc  would  probably  be  worked  by  the  micro- 
organisms which  produce  dental  caries  in  the  mouth;  every  tooth  would 
universally  "decay,"  and  be  promptly  rendered  functionless  and  a 
source  of  danger  to  the  body  generally.  Such  organs  would  never  be 
required.  Scalding  hot  fluids  might  be  taken  into  the  mouth  with 
impunity,  with  obviously  disastrous  effects.  The  sensitiveness  of 
dentine  is  Nature's  protection  to  the  teeth  and  to  the  oral  tissues. 

As  fishes  and  reptiles  have  no  caries-producing  microorganisms  in 
their  mouth,  sensitive  dentine  is  not  wanted.  Hence  many  piscine 
dentitions  are  entirely  tubeless  and  therefore  sensationless.  In  Mam- 
mals, and  particularly  the  lower  Mammals  in  natiird  ferd,  it  is  possible 
also  that  dentine  is  practically  insensitive.  But  in  Man  the  abundant 
distribution  of  the  sensory  nerve  fibres  in  the  pulp  is  quite  remarkable, 
much  more  than  is  needed  for  the  mere  purpose  of  acting  as  trophic 
agents  for  that  organ.  This  question  of  pain  in  the  teeth  is  very  com- 
plex, because  it  may  be  partly  conveyed — in  a  mechanical  sense — by 
the  matrix  of  the  dentine,  as  well  as  by  the  contents  of  the  dentinal 
tubes.      Of  the  latter  we  know  but  little,  of  the  former  nothing. 

In  section  the  dentine  presents  innumerable  channels  which  become 
smaller  as  they  pass  centrifugally  outwards.  There  are  probably  no 
nerves,    neither    medullated    nor    non-medullated    in   dentine.*      The 

*  Since  this  was  written,  Mr.  Howard  Mummery,  whose  researches  on  the  calcification  of  dentine 
are  well  known,  has  communicated  to  the  Royal  Society  a  paper  dealing  with  the  innervation  of 
human  dentine.  By  the  use  of  various  metallic  impregnation  stains,  notably  those  of  Ramon  y 
Cajal,  he  has  demonstrated  the  presence  of  delicate  beads  or  dots  in  the  dentinal  tubules.  As  yet, 
however,  the  paper  has  not  been  published;  suffice  to  say  that  he  is  of  the  opinion  that  the  medul- 
lated nerve  fibres  of  the  pulp  lose  their  medullary  sheaths  as  they  approach  the  plexus  of  Rasch- 
kow,  whence  they  pass  between  and  around  the  odontoblasts  to  a  narrow  marginal  plexus  from 
which  they  enter  the  dentinal  tubes,  and,  accompanying  the  dentinal  processes  of  the  odontoblasts, 
extend  outwards  to  the  extremities  of  the  tubes,  beneath  the  enamel  and  cementum. 


THE  SENSITIVENESS  OF  TEETH  309 

tubules  are  filled  during  life  with  a  protoplasmic  exudation  from  the 
pulp,  which  bathes  the  peripheral  processes  of  the  odontoblasts  on 
its  surface. 

Many  theorists  and  physiologists  differ  in  their  views  as  to  the 
actual  causation  of  sensation.  Thus  some  maintain  that  osmosis 
occurs  in  the  dentinal  tubules,  that  drugs  can  produce  it.  Water  is 
abstracted  or  added  to  the  contents  of  the  tubules,  as  by  the  action  of 
alcohol  or  sugary  compounds,  and  pain  results.  Others,  the  hylop- 
athists,  consider  that  abnormal  movements  in  the  molecules  of  the 
dentinal  fibrils  may  occasion  it.  Others,  that  an  elevation  or  a  lower- 
ing of  the  pressure  in  the  pulp  cavity  itself  will  evidence  it.  Others, 
again,  that  convection  may  take  place  in  these  fibrils  as  on  the  appli- 
cation of  a  stream  of  heated  air;  and  finally  others,  that  certain  obscure 
electrical  reflexes,  similar  to  the  demarcation  currents  observed  during 
injury  to  a  muscle,  may  produce  it.  It  is  difficult  to  determine  the 
truth;  and  at  present  it  is  impossible  to  make  a  clear  specific  statement 
on  the  matter,  unless  and  until  Howard  Mummary's  observations  are 
fully  accepted. 

It  would  probably  be  true,  however — it  remains  for  future  obser- 
vations to  determine — that  the  nervous  perceptions  of  a  tooth  are  so 
high  and  so  complex  from  a  physiological  point  of  view,  that  the  pulp 
may  be  considered  to  be  a  very  special  sense  organ,  ranking,  not  equally, 
but  in  some  considerable  degree  or  manner,  with  those  of  the  special 
senses  of  hearing,  of  sight,  and  of  taste  themselves.  Moreover,  it  must 
not  be  forgotten  that  a  tooth  is  essentially  a  unique  structure,  having 
in  its  interior  a  highly  sentient  body,  and  on  its  periphery  an  inert, 
dead,  irresponsive  material  with  an  intermediate  region  of  semivital- 
ized,  semiperceptive  tissue,  of  which  the  like  exists  in  no  other  portion 
of  the  human  economy.  Microscopically,  it  is  probable  that  nothing 
occupies  a  dentinal  tube  except  lymph  and  the  dentinal  fibril,  which 
usually  on  account  of  reagents,  has  shrunk  to  or  near  its  axial  parts. 
As  this  is  protoplasmic  in  character  and  nervous  in  function,  and  is 
part  of  an  odontoblast,  it  follows,  if  these  premises  are  correct,  that 
the  syllogism  is  completed  by  concluding  that  the  odontoblast  is  a 
sensation  transmitter,  and  an  end  organ  of  the  non-medullated  nerve 
fibres  of  the  pulp,  its  fibril  or  fibrils — for  there  may  be  more  than  one 


310  THE  FUNCTIONS  OF  THE  DENTAL  TISSUES 

from  one  cell — the  dendron  or  dendrons  and  its  ultimate  branchings, 
the  dendrites. 

Cementum. — It  has  been  frequently  asserted  that  cementum  is 
sensitive.  It  is  probable  that  this  is  an  erroneous  belief.  This  tissue 
does  not  require  a  nervous  supply,  and  nothing  in  the  shape  of  nerves 
have  ever  been  demonstrated  in  its  substance.  It  is  very  thin  and  is, 
normally,  practically  structureless,  the  amount  of  its  protoplasmic 
content  being  almost  a  negligible  quantity.  The  hypothesis  of  sensi- 
tiveness in  cementum  probably  arose  from  the  fact  that,  when  exposed 
by  absorption  of  bone,  the  roots  of  teeth — e.  g.,  the  palatine  roots  of 
the  maxillary  first  and  second  molars — may  at  times  have  painful 
sensations  relegated  to  them.  It  is  more  than  likely  that  this  is  due 
either  to  transmission  of  sensations  through  it  to  the  radicular  pulp, 
in  an  analogous  manner  to  that  which  obtains  in  the  enamel,  or  to 
exposure  of  the  free  margin  of  the  periodontal  membrane  which  has 
become  diseased;  or  it  may  be  a  combination  of  the  two. 

Not  only  is  a  tooth  anatomically  and  physiologically  a  unique  organ, 
but  the  suffering  it  experiences  through  exposure  of  its  dentine  by 
caries,  or  as  a  consequence  of  the  effects  of  a  vascular  legion  of  the 
pulp,  is  also  unique.  It  is  a  common  clinical  experience  to  find  a  cavity 
of  "decay"  well  advanced  before  any  symptoms  of  pain  (odontalgia) 
have  exhibited  themselves.  On  the  other  hand,  the  reverse  may  often 
be  met  with. 

In  the  same  individual  two  or  more  types  of  pain-emitting  phe- 
nomena may  occur  simultaneously.  Attention  may  be  directed, 
because  of  the  discomfort  which  is  experienced,  to  a  deep  cavity  in 
which  a  filling  has  become  shrunken  or  loosened,  and,  close  by,  or  in 
another  region  of  the  mouth,  there  may  be  a  similarly  deep  excavation 
of  the  hard  tissues,  of  which  the  individual  knows  nothing.  What 
physiological  and  pathological  processes  are  at  work  in  these  circum- 
stances?   Who  can  explain  these  conditions? 

Recent  investigations  in  the  physiology  of  the  nervous  system  of  the 
body  generally,  and  particularly  of  the  sensory  nerves,  would  tend  to 
show  that  the  method  of  conveyance  of  sensations  to  the  brain  by  the 
ordinary  routes  is  not  so  simple  as  has  hitherto  been  believed.  Pro- 
fessors Sherrington  and  Head  have  demonstrated  that  both  the  motor 


THE  SENSITIVENESS  OF  TEETH  311 

and  the  sensory  nerves  act  in  a  somewhat  complex  fashion.  The  old 
theory  held  that  if  a  series  of  definite  impulses  was  applied  to  certain 
parts  of  the  body,  the  sensory  nerves  conducted  the  impressions  to  the 
brain,  where  they  were  either  made  known  to  the  mind  of  the  individual 
only,  or  were  immediately  responded  to  by  the  motor  nerves.  Thus, 
if  the  hand  is  plunged  into  warm  water,  a  sensation  of  pleasurable 
warmth  is  experienced,  or  if  the  water  be  too  hot  the  hand  is  at  once 
withdrawn  on  account  of  the  painful  impressions  made  upon  the 
sensorium. 

But  it  has  been  found  that,  though  sensations  do  travel  to  the  brain, 
they  do  not  all  journey  at  the  same  rate.  In  other  words,  they  prob- 
ably race  one  another,  and  that  sensation  which  reaches  the  cerebral 
convolutions  first,  shuts  out  the  others  from  competition,  so  to 
speak,  in  much  the  same  way  as  a  horse  which  has  won  a  race.  The 
sensations  which  start  from  the  periphery  when  the  hand  is  placed  in 
pleasurably  warm  water  are  of  various  kinds,  and  the  sense  of  pleasant 
warmth  is  that  one  which  reaches  the  brain  first.  By  means  of  a 
suitably  contrived  apparatus  it  is  possible  to  prevent  this  sensation 
winning  the  race,  and  if  used  in  appropriate  conditions,  when  the  hand 
is  plunged  into  pleasurably  warm  water,  the  first  impulses  which  reach 
the  brain  are  those  which  give  rise  to  the  sensation,  not  of  warmth, 
but  of  pain ! 

The  hypothesis  which  can  be  based  upon  this  experiment  would  lead 
one  to  believe  that  the  evolution  of  the  sensory  nerves  in  the  human 
organism  has  continually  been  in  the  direction  of  the  avoidance  of 
giving  the  human  being  pain.  The  nervous  system  has  been  compared 
to  a  "bankrupt  telephone  exchange,"  in  which  nerve  and  sensation  are 
hardly  ever  related,  the  seat  of  pain,  and  its  cause,  being  united  by  a 
bewildering  system  of  so-called  "way-leaves."  Some  of  the  abdominal 
viscera,  such  as  the  liver  or  pancreas,  possess  a  nervous  mechanism 
which  evolution  has,  rendered  insensitive;  the  result  being  that  the 
existence  of  an  injury  of  one  of  these  organs  has  to  be  diagnosed,  not 
from  the  direct  pain  in  the  parts,  but  by  totally  different  subjective 
and  objective  symptoms.  Physiological  telephoning,  unlike  the  real 
thing,  is  hardly  ever  direct;  communications  have  to  be  made  in  all 
sorts  of  round-about  ways. 


312  THE  FUNCTIONS  OF  THE  DENTAL   TISSUES 

It  may  be  possible  that  herein  hes  the  explanation  of  the  existence 
of  the  sensation  of  discomfort  which  is  constantly  perceived  by  the 
teeth,  as  distinct  from  the  usual  pain  of  a  neuralgic  character. 


DENTAL    PAIN 

The  dentine  is  said  to  have  an  area — presumably  that  occupied  by 
the  interglobular  spaces — near  its  surface  peculiarly  liable  to  set  up 
symptoms  of  pain.  Dental  pain  is  without  a  like  or  equal,  and  differs 
from  that  elsewhere.  If  a  decapitated  frog  should  have  an  irritant 
applied  to  the  skin  of  its  leg — a  well-known  experiment — it  will,  though 
unable  to  become  aware  of  pain,  at  once  retract  that  extremity  and 
endeavour  to  get  rid  of  the  source  of  offence,  a  proof  of  the  existence, 
here,  of  a  reflex  mechanism  which  resides  over  the  nerve  supply  of 
that  part.  Now  pain  was  evolved  for  the  benefit  of  the  organism 
which  perceives  it.  Pain  is,  in  its  origin,  a  magnificent  protection. 
But  in  the  teeth  there  are  no  evidences  of  definite  and  direct  reflex 
arrangements  being  made  by  Nature  for  the  removal  of  irritants 
without  any  association  with  sensation,  as  in  the  frog  for  instance,  or 
elsewhere,  such  as  the  cornea,  the  skin,  etc.  The  beneficence  of  pain 
in  the  teeth  is,  therefore,  very  slight;  in  other  parts  of  .the  body  it  is 
very  great.  If  pain  did  not  exist,  the  teeth  would  share  the  same  fate 
that  other  organs  would  undergo  under  similar  conditions,  and  would 
be  rapidly  destroyed;  but,  as  its  protective  influence  is  a  modified 
one — it  is  frequently  hypalgesic — many  cases  occur  where  destruction 
goes  on  without  its  making  itself  felt.  A  reflex  act  is  not  required 
here,  and  is  non-existent.  In  the  teeth  it  would  appear  that  pain  is 
an  epiphenomenon,  and  not  causally  related  to  the  conditions  that 
naturally  obtain  in  other  regions. 

Fully  aware  that  the  above  views  are  widely  divergent  from  those 
commonly  held,  the  author  has  set  them  down  nevertheless,  in  the 
earnest  belief  that,  while  open  to  modification,  they  are,  in  the  main, 
correct. 

The  sensitiveness  of  the  teeth  diminishes  with  advancing  age.  For 
anatomical  reasons  it  is  naturally  more  acute  in  the  young.     Exposure 


DENTAL  PALY  313 

of  the  pulp  in  the  aged  is  practically  unattended  by  symptoms  of 
severe  if  any  pain.  The  cause  is  plain  and  not  far  to  seek.  If  the 
apical  regions  of  any  tooth  removed  from  the  mouth  of  a  middle-aged 
person  be  examined,  it  will  commonly  be  observed  that  the  apical 
foramina,  which  transmit  the  afferent  arteries  and  nerves  and  the 
afferent  veins,  is  almost  invisible.  They  have  in  the  course  of  time 
become  extended.  Normal  closure  of  the  apices — that  is  the  physio- 
logical cessation  of  growth  of  the  extremities  of  the  roots  occurs — 
as  far  as  can  be  at  present  ascertained — as  follow: 

Maxillary  Series:  First  incisor,  twelfth  year,  second  incisor  twelfth 
year,  canine  fourteenth  year,  first  premolar  thirteenth  year,  second 
premolar  thirteenth  year,  first  molar  twelfth  year,  second  molar 
seventeenth  year,  third  molar  nineteenth  to  twenty-fifth  year. 

Mandibular  Series:  First  incisor  eleventh  year,  second  incisor 
twelfth  year,  canine  fourteenth  year,  first  premolar  thirteenth  year, 
second  premolar  thirteenth  year,  first  molar  eleventh  year,  second 
molar  eighteenth  year,  third  molar  twenty-first  year  to  twenty-fifth 
year.  But  after  the  age  of  thirty  years  these  open  canals  become 
generally  less  patent,  until  at  and  above  fifty — to  make  a  shrewd  con- 
jecture— the  pulps,  cut  off  from  their  usual  trophic  suppl}-,  are  degen- 
erated and  presence  of  pain  slowly  modified  and  diminished.  It  is 
extremely  probable  that  after  the  age  of  thirty-five  the  teeth  of  the 
ordinary  European,  American  or  Asiatic  individual  possess  degenerated 
and  only  slightly  sentient  pulps. 

Referenxes 

1.  Barker.     "The  Nervous  System,"  1901. 

2.  Haeckel.    "The  Evolution  of  Man,"  1874. 

3.  Hopewell-Smith.  "The  Histology  and  Patho-histology  of  the  Teeth  and  Associated  Parts," 
1903. 

4.  Korschelt  and  K.  Heider.  "  Lehrbuch  der  vergleichenden  Entwickelungsgeschichte  der 
wirbellosen  Thiere,"  1910. 

5.  Morgenstern.  "  Ueber  das  Vorkommer  von  N erven  in  den  harten  Zahnsubstanzen,  "  Dcjf/if/je 
Monatsschrift  fiir  Zahnheilkunde,  1892;  also  Deutsche  Monatsschrifl  fiir  Zahnheilkuiide,  1895. 

6.  "Nature,"  1911,  vol.  l.xxxvi.  No.  2163. 

7.  Paul.    "Nasmyth's  Membrane,  "  r/je  ZPew/a/ 7?fforrf,  1894. 

8.  Romer.    "  Nerven  in  Zkhnen,"  Zahnhislologische  Sliidie,  1899. 

9.  Tomes.    "A  Manual  of  Dental  Anatomy, "  1898. 
10.  Halliburton.     "Handbook  of  Physiology,"  1900. 


CHAPTER    XVI 
MAMMALIAN   DENTITIONS 

The  General  and  Dental  Characteristics  and  Variations  of  the  Teeth  of  the  Cheiroptera. — Of  the 
Insedivora. — Of  the  Rodeniia. — Of  the  Carnivora. — Of  the  Cetacea. — Of  the  Sirenia. — Of 
the  Ungulata. — Of  the  Edentata. — Of  the  Marsupialia. — Of  the  Monotremala. 

Sub-Class  II.    Eutheria   (continued) 

ORDER  XII.     CHEIROPTERA 

Placed  high  up  in  the  scale  of  mammalian  development,  are  the 
flying  mammals,  known  as  the  Bats  (Cheiroptera:  -Vsio,  hand;  -zspbv, 
wing),  creatures  which  are  more  specialized  even  than  the  numerous 
carnivorous  species  of  animals. 

The  Bats  are  flying  vertebrates,  having  as  wings  a  thin  integumental 
membrane  which  intervenes  between  the  hind  limbs  and  tail,  and  the 
digits  of  the  fore  limbs.  The  radius  is  curved  and  long,  the  ulna 
elementary.  The  membrane  is  provided  with  vascular  and  nervous 
systems,  and  lies  chiefly  between  the  second  and  fifth  digits,  which 
are  enormously  long.  The  mammae  are  thoracic,  and  the  smooth 
cerebral  hemispheres  do  not  extend  over  the  cerebellum.     (Bedhard.) 

The  order  is  divisible  into  two  primary  groups,  of  which  each  is 
further  subdivided.     These  are  known  as: 

Sub-order    I.     Megachiroptera  {iJ-syaz,  great — Xs.l[>,  -ztpm),  of  which  the 

most  important  Family  is  the  Pteropodice. 
Sub-order  II.     Microchiroptera  {luxim:,  small),  which  includes: 

Rhinolophidce 

NycteridcE 

Vespertilionidce 

EmballonuridcB 

PhyllostomatidcB 


CHEIROPTERA  315 

Of  these  the  Megachiroptera  are  frugivorous  bats,  of  large  size,  and 
the  Microchiroptera  are  mostly  insectivorous,  but  in  some  species 
frugivorous  and  sanguinivorous. 

Comprised  in  the  former  is  the  Pteropus  (Fox-bat).    There  are  about 

sixty  species.     It  is  commonly  found  in  India,  Madagascar,  Australia, 

Queensland,  etc. 

Fig.  299 


111 
Skull  of  a  frugivorous  bat  {Pteropus  fuscus).     X  to- 

Dental  Characteristics. — The  incisors  are  small,  the  molars  large, 
with  intervals  between,  and  not  tubercular,  but  divided  by  a  longitu- 
dinal ridge.    The  teeth  are  haplodont,  and  flattened  from  side  to  side. 

The  Microchiroptera  include  four  hundred  species,  and  are  dis- 
tinguished by  the  presence  of  "nose-leaves"  which  act  as  tactile  organs. 
In  this  group  are  placed  the  False  Vampires,  the  Horseshoe  bats,  the 
White  bat,  the  Vampire,  or  blood-sucking  bat  {Desmodiis),  which  is 
capable  of  sustaining  its  life  by  gorging  the  blood  of  man  and  animals. 
Its  oesophagus  is  too  narrow  to  allow  more  than  a  fluid  diet  to  pass. 

Normal  Type. — The  incisors  are  small,  the  canines  large,  the  pre- 
molars and  molars  possess  sharp  cusps,  and  present  a  W-shaped  pattern 
of  their  ridges. 

Aberrant  Type. —  Desmodus,  the  Common  Vampire,  has  a  large, 
permanent  upper  incisor,  which  is  prismatic  in  form,  in  each  jaw. 
The  canine,  smaller  than  the  preceding,  is  sharp,  and  pointed  and 
large.  The  molars  are  stunted  in  growth,  and  diff^er  but  slightlj-  in 
their  configuration  from  the  premolars. 


316  MAMMALIAN  DENTITIONS 


ORDER   XI.    INSECTIVORA.    {Insecta — insects,   vorare — to    devour.) 

Sub-order  Family 

(i  )  Dermoptera  Galeopithecidce  (Flying  Lemurs) 

(ii)   Insectivora  vera       Erinaceidce  (Hedgehogs) 

Tupaiidce  (Tree-shrews) 

CantetidcB  (Tenrecs) 

Potamogalidce  (Potamogales) 

SohnodontidcB  (Solemodons,    fish-eaters  as 

well  as  insectivorous) 

ChrysochloirdcE  (Golden  moles) 

MacrosceUdce  (Jumping  shrews) 

TalpidcB  (Moles) 

Soricidce  (Shrews) 

In  geographical  distribution  insect-eating  mammals  are  found  in 
North  America  and  the  Old  World.  They  are  absent  from  the  con- 
tinents of  Australia,  South  America,  and  the  Islands  of  Japan.  In 
South  America  the  Marsupial  opossum  corresponds  to  this  order. 

The  Insectivora  are  all  small  vertebrates,  the  great  majority  being 
nocturnal  in  habit,  and  their  ancestry  very  ancient,  suppression  of 
some  of  the  deciduous  teeth  pointing  to  this.  The  limbs  usually 
possess  five  digits.  Clavicles  are  present  as  a  rule.  The  dental  char- 
acteristics are  fairly  regular,  the  typical  mammalian  dentition  being 
very  common.  Most  cheek  teeth  are  trituberculate,  again  indicating 
the  antiquity  of  the  group. 

General  Dental  Characteristics. — Normal  Type. — There  are  never 
less  than  four  mandibular  incisors  in  any  of  the  species,  the  first  incisors 
are  often  larger  than  the  second,  the  canines  are  usually  smaller  than 
the  former,  no  "carnassial"  tooth  is  present,  and  the  crowns  of  the 
molars  are  surmounted  by  a  number  of  cusps  which  are  arranged  in 
V-shaped  ridges  in  the  Golden  Mole,^  W-shaped  ridges  in  the  Mole, 
and  themselves  are  triangular  and  tricuspid  in  pattern  in  the  first- 
named  and  quadrangular  in  the  hedgehogs,  moles,  and  shrews.  The 
dentition  is  diphyodont,  and  the  teeth  are  heterodont.-" 


RODENTIA  317 

Aberrant  Type. — The  controversial  nature  of  the  dental  formula 
of  the  Mole-  has  already  been  alluded  to.  Its  eyes  are  rudimentary. 
It  eats  insects  and  earthworms.  It  is  calculated  that  one  mole  can  eat, 
independently  of  other  food,  20,000  earthworms  in  a  year,  and  hence, 
like  many  of  the  insectivora,  is  e.xceedingly  voracious.  If  kept  without 
food,  or  unable  to  obtain  it  for  a  period  of  twenty-four  hours,  it  dies 
of  hunger.  It  adopts  in  extreme  cases  of  exhaustion  a  curious  subter- 
fuge, and  is  said  actually  to  catch  birds,  by  burying  itself  in  a  mole- 
hill, and  moving  its  muzzle  continuously  to  and  fro,  just  beneath 
the  surface,  to  attract  any  incautious  bird  which  may  be  deceived  by 
thinking  that  it  is  an  earthworm  that  is  stirring. 

The  Shrews  have  tubular  enamel,  which  is  also  greatly  pigmented. 
On  the  authority  of  Sir  W.  Flower,  adult  shrews  exhibit  the  unusual 
condition  of  anchylosis  of  their  incisors  to  the  bones  of  the  jaw.  Ves- 
tigial remains  have  been  discovered  in  association  with  these  teeth. 

The  Galeopithecus  volans  has  pectinate  incisors.  Its  dental  formula 
according  to  Leche,  is    I  |  C  -I  Pm   |  M  f  X  2  =  34. 

The  second  incisor  is  bi-rooted. 


ORDER    X.      TILLODONTIA    {ri'/lco — to  tear;  odouz — tooth) 
Extinct  rodents. 


ORDER  IX.     RODENTIA   (Rodere— -to  gnaw) 

The  rodents  comprise  nearly  a  thousand  known  species.  In  dis- 
tribution they  are  cosmopolitan,  most  chiefly  located  in  South  America, 
while  Australia  has  but  few  genera.  All  are  exclusivel}-  herbivorous, 
and  obtain  their  food  by  gnawing.  While  they  are  generally  terrestrial, 
some  are  aquatic — such  as  the  beaver  and  water  vole;  some  arboreal 
— such  as  the  squirrel;  some  are  cursorial,  such  as  the  hare;  some 
fossorial,  such  as  the  mole-rat. 

In  the  skull  the  zygomatic  arch  is  invariably  present,  and  the 
orbit  is  not  separated  by  a  bony  rim  from  the  temporal  fossa.  An 
extended  diastema  is  universal,  and  intervenes  between  the  incisors 
and    premolars    or    molars.     The    palate    is    narrow    in    an    antero- 


318 


MAMMALIAN  DENTITIONS 


posterior   direction,    and    the    mandible    possesses    a 
process  and  a  great  development  of  the  angle. 


small    coronoid 


Sub-order 


(i)  Simplicidentata 


Section  I.     Sciuroniorpha 

Family: 

A  nomaluridcB 

SciiiridcB 

Castoridce 

HaplodontidcB 

Section  II.     Myomorpha 

Family : 

Gliridce 

MuridcB 

BathyergidcB 

SpalacidcB 

Geomyidce 

HeteromyidcB 

DipodidcB 

PedetidcB 


(Squirrel-like) 


(Squirrels) 
(Beavers) 

(Mouse-like) 

(Dormice) 
(Rats,  mice) 
(Cape-moles) 
(Bamboo-rats) 
(Pouched  rats) 
(Kangaroo  rats) 
(Jerboas) 


Section  HI.     Hystricomorpha  (Beaver-like) 

Family : 

OctodontidcE 

Ctenodactylidce 

Caviidce 

Dasyproctidce 

Dinomyidce 

ChinchillidcB 

Cercolabidce 

HystricidcB 


(Water-rat) 

(Capybaras,  cavies) 
(Spotted  cavies,  agoutis) 

(Chinchillas) 
(Tree  porcupines) 
(Porcupines) 


General  Dental  Characteristics. — Normal  Type. — Rodents  are  gen- 
erally diphyodont,  but  rats  and  mice  are  probably  monophyodont. 

The  dental  formula  is  very  constant:   I  i  C  ^  Pm  I  M  -f  X  2  =  20. 

The  incisors  are  scalpriform  or  chisel-shaped,  grow  from  persistent 
pulps,  and  are  curved,  the  curvature  of  the  maxillary  teeth  being  some- 
what greater  than  that  of  the  mandibular  series.      The  anterior  surfaces 


CREODONTA  319 

only  are  covered  with  enamel,  which  is  usually  of  a  very  complex 
pattern  and  at  times  highly  pigmented.  Canines  are  never  present. 
The  molars  may  be  entirely  rootless  or  rooted,  their  crowns  tuber- 
culated,  bunodont,  or  lophodont.  The  enamel  is  tubular  in  the  jerboas. 
The  movements  of  the  mandible  are  restricted  to  forward  and  back- 
ward direction.  Hence  the  presence  of  the  long  diastema,  which 
probably  also  serves  as  a  cheek  pouch  for  the  storage  of  food,  and  at 
the  same  time  allows  the  incisors  to  attain  their  usual  enormous 
length. 

Aberrant  Type. — In  Tlydromys  {'jScop — water;  ,«'^c — mouse)  there' 
is  a  reduction  in  the  number  of  the  incisors  and  molars,  and  pre- 
molars are  absent.     The  formula  is:    I  t  C  |^  Pm  |  M  |X2=  12. 

Sub-order  Family 

(ii)  Duplicidentata  Leporidce  (Rabbits,  hares) 

LagomyidcB  (Pikas  and  calling  hares) 

These  are  distinguished  from  the  former  sub-orders  and  Families 
by  the  presence  of  two  extra-maxillary  incisors,  placed  behind  the  large 
curved  ones. 

The  hare  presents  an  unusuall}'  large  number  of  teeth  for  a  rodent, 
its   formula  being:    I  f  C  ^  Pm  |  M   |  X  2  =  28. 

Fig.  300 


The  skull  of  a  hare  {Lepus  europcsus).     X  i. 


ORDER    VIII.      CREODONTA    (A>£«c— flesh;   ddou;— tooth) 
Extinct  carnivores 


320 


MAMMALIAN  DENTITIONS 


ORDER    VII.    CARNIVORA    {caro— Resh;  vorare— to  eat) 

This  Order  consists  of  small  and  large  quadrupeds,  of  usually  car- 
nivorous habits.  They  may  be  terrestrial,  arboreal,  or  aquatic.  The 
teeth,  generally,  have  sharp  and  cutting  edges,  the  incisors  are  small 
and  canines  large.  The  toes  are  never  less  than  four  in  number;  the 
claws  usually  being  long  and  sharp.  Clavicles  may  exist  in  an 
incomplete  form,  or  they  may  be  entirely  absent.  The  brain  is  well 
developed,  and  the  cerebral  hemispheres  present  numerous  convolutions. 
The  stomach  is  always  simple,  and  the  cecum,  when  present,  small. 


Sub-order 

(i)  Fissipedia  (cleft- 
feet)  (Terrestrial) 


(ii)  Pinnipedia  (fin- 
feet)  (Aquatic) 


Family 

Felidce 

MachcErodontidce 

VivveridcB 

Hycenidce 

Canidce 

Procyonidce 

Miistelidce 

Ursidce 

OtariidcB 

Trichechidce 

Phocidce 


(Lions,  tigers,  cats,  leopards) 

(Civets) 

(Hyaenas) 

(Dogs,  foxes,  wolves) 

(Raccoons) 

(Badgers) 

(Bears) 

(Sea  lions) 
(Walrus) 
(True  seals) 


General  Dental  Characteristics. — Normal  Types. — (?)  Fissipedia. 
Somewhat  small  in  size,  the  incisors  are  almost  invariably  six  in  number; 
the  canines  are  large,  strong,  and  always  present.  The  last  maxillary 
premolar  (Pm^  and  ''Pm)  and  the  first  permanent  mandibular  molar, 
(Ml  and  iM)  are  "carnassial"  or  "sectional"  teeth,  which  are  often 
much  larger,  and  much  longer,  than  the  other  premolars  and  molars, 
those  in  front  of  the  "  carnassials"  being  small  and  cone-shaped,  those 
behind  tuberculated,  and  with  broad  crowns.  The  simpler  cheek 
teeth  are  frequently  trituberculate,  others  multituberculate. 

In  the  primitive  type  of  carnivora  the  skull  is  larger  than  in  the 
more  specialized  forms,  such  as  the  Felidce.     There  is  no  soft  palate. 


CARNIVORA 


321 


The  mandible  has  an  elevated  coronoid  process,  and  the  condyle, 
almost  cylindrical,  is  elongated  in  its  transverse  diameter,  and  fits 
ver}^  closely  into  the  glenoid  cavity. 


Fig.  301 


]a.ws  oi  3.lion  {Felis  leo).     X  -3.     The  jaws  are  placed  side  by  side  to  show  their  relative  proportions. 


There  are  no  typical  carnivores  in  Madagascar  or  Australia.  The 
dental  formula  in  the  Felidce  is:  I  |  C  f  Pm  f  or  |  M  y  X  2  =  28  or  32. 

In  this  Family  the  blade  of  the  maxillary  carnassial  is  trilobed,  and 
the  mandibular  molar  has  no  internal  cusp. 

These  are  typically  carnivorous.  Lions  may  attain  the  age  of 
seventy  years,  cats  fifteen. 

The  extinct  cats  {Machccrodontida:;  (ui-y/una — a  sword  or  sabre) 
include    the    "Sabre-toothed    Tigers,"    creatures    who    had    enormous 


322 


AiAMMALIAN  DENTITIONS 


maxillary  canines,  the  possession  of  which  probably  caused  the  extinc- 
tion of  the  species,  inasmuch  as  these  teeth  were  of  such  huge  dimen- 
sions that  they  probably  became,  as  Flower  suggests,  an  inconvenience 
and  hindrance  to  their  owners.  They  could  not  be  used  as  cutting 
instruments,  and  greatly  interfered  with  the  act  of  feeding. 

The  genera  of  Civets  differ  very  considerably  in  their  dental  formulae: 
the  majority  possess  a  greater  number  of  teeth  than  the  cats. 

Fig.  302 


The  same — side  aspect.      X  3. 


Hycenas  are  noted  for  the  possession  of  an  additional  maxillary 
premolar.  External  and  internal  cingula  are  found,  as  has  already 
been  described. 

An  aberrant  type  of  the  Hymiidce  is  the  Aard-wolf  of  South  Africa, 
where  the  molars  and  premolars  are  rudimentary  and  ill-developed. 

Dogs,  Wolves,  etc.,  have  the  following  formula: 

I  I  C  I  Pm  ^  M  1^^  X  2  =  40  or  44. 

Dogs  are  typical  mixed  feeders,  and  have  large  carnassials,  with  a 
talon  or  tubercle  on  the  mandibular  corresponding  tooth.^  *  ^^ 

An  almost  typical  mammalian  dentition  is  met  with  in  the  Bears, 
the  difference  being  that  there  are  only  two  maxillary  molars..  In 
adults  second  and  third  premolars  are  shed,  thus  forming  the  exception 


CARNIVORA 


323 


to  the  rule,  that  when  premolars  are  lost,  it  is  from  the  anterior  end  of 
the  series  that  the  loss  takes  place.     The  carnassials  are  degenerated. 


Fig.  303 


Jaws  of  a  typical  civet  {Viverra  civetta).     X  *.    The  jaws  are  placed  side  by  side  to  show 
their  relative  proportions. 

Fig.  304 


^/ 


H4 


Skull  of  a  long-muzzled  dog  (Ca«/5/anr/7/arii).      X  5. 

The   brown    bear   eats    roots,    fruit,    sometimes    carrion,    honey,    and 
ants.      The    Badger  {Meles)    possesses  thirty-eight   teeth.     The  first 


324 


MAMMALIAN  DENTITIONS 


premolar  is  very  small,  and  often  early  shed,  the  maxillary  molar  is  a 
large  quadrangular  tooth,  as  broad  as  it  is  long,  far  surpassing  the 
"carnassial"  in  size.  The  mandible  is  so  firmly  articulated  to  the 
glenoid  cavity  that  it  cannot  be  separated  without  fracture. 

The  American   Raccoons  are  small   carnivores,   with  short,   broad, 
maxillary  "carnassial"  teeth  and  two  pairs  of  molars  in  each  jaw. 


Fig.  305 


Jaws  of  a  sea  otter  {Latax  lulris).     X  s-    The  jaws  are  placed  side  by  side  to  show  their 
relative  proportions. 

Aberrant  Type. — The  Sea-otter  has  a  formula: 
I  f  C  1  Pm  f  M  i  X  2  =  32. 

Here  the  jaws  are  short,  and  the  teeth  are  large,  the  molars  having 
flattened  and  rounded  crowns.  It  eats  crabs,  sea-urchins,  and,  at 
times,  small  tish.  The  shells  are  crushed  by  means  of  the  flat-topped 
molars,  being  held  by  its  fore-paws. 


CARNIVORA  325 

(ii)  Piun/pcdia.  The  deciduous  dentition  is  feeble  and  shed  at  an 
early  period  of  growth:"  there  is  a  tendency  to  a  homodont  type  in 
the  pattern  of  the  cheek  teeth:  there  are  no  "carnassial"  teeth:  the 
number  of  incisors  is  reduced  below  the  typical  number. 

The  great  majority  are  canine,  and  most  feed  on  fish  and  crustacese. 


Fig.  306 


Skull  of  a  brown  bear  (Ursiis  arctus 


According  to  Mr.  W.  H.  Elliott" — "The  fighting  between  the  old 
male  eared-seals  for  possession  of  the  cows  is  entirely  done  with  the 
mouth.  The  opponents  seize  one  another  with  their  teeth,  and  then, 
shutting  their  jaws,  nothing  but  the  sheer  strength  of  the  one  and  the 
other  tugging  to  escape  can  shake  them  loose,  and  that  effort  invari- 
ably leaves  an  ugly  wound,  the  sharp  canines  tearing  out  deep  gutters 
in  the  skin,  and  furrows  in  the  blubber,  or  shredding  the  flippers  into 
ribbon-strips.  The  bulls  generally  approach  each  other  with  comically 
averted  heads,  just  as  though  they  were  ashamed  of  the  rumpus  which 
they  are  determined  to  precipitate.  When  they  get  near  enough  to 
reach  one  another,  they  enter  upon  the  repetition  of  many  feints  or 
passes  before  either  the  one  or  the  other  takes  the  initiative  by  gripping. 
The  heads  are  darted  out  and  back  as  quick  as  a  flash;  their  hoarse 
roaring  and  shrill  piping  whistle  never  ceases,  while  their  fat  bodies 
writhe  and  swell  with  exertion  and  rage;  furious  lights  gleam  in  their 
eyes;  their  hair  flies  off  into  the  air,  and  their  blood  streams  down. 
All  this  combined  makes  a  picture  so  fierce  and  so  strange  that,  from 


326 


MAMMALIAN  DENTITIONS 


its  unexpected  position  and  its  novelty,  this  is  one  of  the  most  extraor- 
dinary brutal  contests  man  can  witness." 

The  Walrus  presents  a  remarkable  difference  in  its  dentition  from 
the  seals.  The  maxillary  canines  are  developed  into  enormously  long 
tusks  which  are  persistently  growing  (Tomes").  They  project  far 
beyond  the  lips  and  below  the  lower  jaw.  The  molars  have  flattened 
crowns,  and,  with  the  premolars,  are  small,  simple,  and  single-rooted. 
The  tusks  are  used  for  raking  out  of  the  mud,  certain  shell-fish, 
on  two  species  of  which  they  live  entirely. 

The  formula  probably  is:  I  i  C  x  Pm  |  x  2  =  18. 

Fig.  307 


Skull  of  an  eared  seal  {Otaria). 


The  true  Seals  are  best  adapted  for  aquatic  life.  External  ears  are 
wanting.  Every  species  has  five  pairs  of  cheek  teeth,  the  number  of 
incisors  remaining  variable.  In  the  "grey"  seal  most  of  the  cheek 
teeth  are  single-rooted;  the  typical  seals  have  cheek  teeth,  which  are 
small,  and — excepting  the  first  pair  in  each  jaw — are  implanted  by 
double  roots.     The  crowns  carry  accessory  cusps. 

The  dentition  of  the  Monk-seal  is  characterized  by  the  presence  of 
thirty-two  teeth,  the  crowns  of  the  cheek  teeth  being  hollowed  out 
on  the  internal  aspects,  where  there  is  a  strongly-marked  basal  ledge. 
The  first  cheek  teeth  are  rudimentary. 


CETACEA  327 


ORDER    VI.    CETACEA  (cetiis—a  whale) 

The  Cetaceans  comprise  whales,  sperm-whales,  porpoises,  and  dol- 
phins. They  have  the  following  characteristics  with  other  mammals: 
they  are  warm-blooded,  possess  lungs,  bring  forth  their  young  alive, 
and  feed  them  on  milk.  They,  however,  differ  in  the  fact  that  they 
are  admirably  adapted  for  aquatic  life. 

The  body  is  fish-like — there  is  no  neck.  The  fore  limbs  are  paddles, 
and  exhibit  no  visible  signs  of  being  composed  of  arms,  forearms, 
wrists,  hands,  and  fingers. 

Whales  live  in  all  seas,  some  being  found  in  the  large  rivers  of  South 
America  and  Asia.  Whales,  according  to  an  estimate  of  Cuvier's,  may 
live  more  than  one  thousand  years.  A  whale  born  about  the  time  in 
British  history  when  Alfred  the  Great  was  burning  the  shepherd's 
wife's  cakes,  would  probably  be  alive  at  the  present  day. 

The  "spouting"  of  cetaceans  is  mainl}-  the  condensed  vapour 
"breathed"  through  the  nasal  orifices  which  are  situated  on  the  top 
of  the  head. 

-  The  "Right"  whale  and  the  Walrus  are  fast  disappearing  off  the 
face  of  the  earth,  on  account  of  the  fact  that  the  spread  of  civilization 
tends,  in  the  main,  to  exterminate  certain  forms  of  animal  life,  and 
therefore  gives  value  to  the  oil,  the  ivor}-,  and  the  whalebone  of  these 
mammals. 

Cetacea'  are  "aquatic"  mammals  of  fish-like  form;  tail  expanded 
into  horizontal  flukes;  a  fatt}'  dorsal  "fin"  present  in  most  species; 
anterior  limbs  converted  into  fin-like  paddles;  posterior  limbs  only 
represented  by  skeletal  rudiments.  The  skull  has  a  greatly  developed 
facial  portion;  supra-occipital  bones  meeting  the  frontal,  but  over- 
growing or  growing  in  between  the  parietals;  bones  surrounding  the 
organs  of  hearing  loosely  attached  to  the  skull.  Coronoid  process  of 
mandible  absent,  or  very  feebly  developed.  Teeth,  when  present, 
few  or  numerous,  always  of  simple  conical  form,  with,  at  most,  traces 
of  additional  cusps;  if  absent,  their  place  taken  by  whalebone.  Cer- 
vical vertebrae  of  short  antero-posterior  diameter,  often  more  or  less  . 
completely  welded  together  into  a  single  mass.     Scapulae  peculiarly 


328 


MAMMALIAN  DENTITIONS 


flattened.  Phalanges  of  digits  always  more  numerous  than  in  other 
animals.  Clavicles  absent.  Stomach  complex.  Lungs  simple.  Dia- 
phragm obliquely  set,  and  very  muscular.  Brain  much  expanded 
transversely,  and  well  convoluted.  Mammae  two,  inguinal  in  position. 
They  are  classified  in  three  sub-orders: 


Sub-order 

(  i )  Mystacoceti 

{Mijozaqcixoc;,  moustache, 

cetiis — a  whale) 
Whalebone  whales 
( ii )  Odontoceti  (Toothed 
whales) 


(iii)  ArchcEOceti 


Family 

Balcenopteridce    (Rorquals) 
Balcenidce  (Right  whales) 


Physeteridce         (Sperm  whales  and  beaked 

whales) 
DelphinidcB         (Dolphins,  porpoises) 
PlatanistidcB 

Squalodontidce    (Extinct) 
ZeuglodontidcB    (Extinct) 


A  generalized  cetacean  dentition  is  seen  in  the  Dolphin.  The  teeth 
are  homodont,  conical,  sharp,  curved,  and  very  numerous.  The 
arrangement  of  their  interdigitation  is  splendidly  adapted  for  seizing 
slippery,  living  prey. 

The  Sperm-whale  grows  to  sixty  feet.  It  yields  sperm  oil  in  the 
blubber,  spermaceti  from  a  cavity  in  the  skull,  from  which  are  made 
candles  and  ointments,  and  ambergris,  which  is  a  perfume  issuing 
from  the  intestinal  tract,  and  floating  on  the  surface  of  the  sea. 

Its  dental  armament  is  peculiar,  in  that  in  the  upper  jaw  there  are 
a  few  curved  teeth  partly  buried  in  the  gum,  and  in  the  lower,  the 
deciduous  series,  many  in  number,  persist  throughout  its  life. 

In  the  Beaked  Whales,  there  are  functionless,  rudimentary,  maxillary 
teeth,  and  in  the  mandible,  a  pair,  sometimes  four,  of  thin,  flat,  strap- 
like bodies  which,  as  they  pass  out  of  the  mouth,  are  at  first  straight,, 
but  at  their  terminations,  bent  over  towards  one  another. 


SIRENIA  329 


ORDER  V.      SIRENIA  {Siren— a.  mermaid) 

These  are  "aquatic  mammals  with  but  few  scattered  hairs;  hind- 
limbs  absent,  fore-limbs  paddle-shaped,  tail  flattened,  and  either  whale- 
like or  rhomboidal  to  circular  in  form.  Nostrils  on  upper  surface  of 
not  specially  elongated  snout.  Clavicles  are  absent.  The  scapula 
has  the  normal  mammalian  form,  with  a  well-developed  and  roughly 
median  spine.  The  bones  of  the  arm  and  hand  articulate  together  as 
in  land  animals;  the  phalanges  show,  at  most,  traces  of  increase  in 
number  above  the  normal.  Pelvis  represented  by  a  vestige.  Stomach 
complex,  lungs  simple  and  not  lobulated.  Diaphragm  oblique  and 
very  muscular.  Brain  peculiar  in  form,  and  but  slightly  convoluted. 
Mammae  two,  and  pectoral  in  position."'' 

There  is  but  one  family  Manatidce.  It  includes  the  Manatee  (manus 
— a  hand,  probably  because  it  uses  its  front  limbs  somewhat  in  the 
manner  of  hands),  which  is  found  in  West  African  waters  and  the 
rivers,  and  on  the  shores  of  Eastern  America. 

General  Dental  Characteristics. — It  has  a  large  number  of  molars, 
which  goes  on  increasing  indefinitely  during  the  life  of  the  animal. 
They  undergo  attrition  on  account  of  the  character  of  the  food,  which 
is  mainly  algae,  with  sand  intermixed.  As  many  as  twenty  molars 
have  been  found  in  half  of  each  jaw,  but  only  six  or  eight  are 
present  at  one  time,  and  they  resemble  somewhat  the  molars  of 
the  tapir  {q.  v.).  In  the  front  of  the  mouth  horny  plates  exist, 
covering  up  four  rudimentary  incisors  in  each  jaw. 

The  enamel  rods  run  in  a  straight  line;  the  dentine  at  the  outer 
surface,  according  to  Tomes,"  is  permeated  with  canals  of  large  size — 
which  may  have  presented,  in  ancestral  forms,  a  kind  of  vaso-dentine. 

The  Dugong  lives  in  the  Indian  ocean,  being  fonder  of  deep  water 
than  the  Manatee.  It  is  not  fluviatile.  The  maxillae  are  bent  at  an 
angle,  and  carry  two  tusk-like  incisors  on  the  prominent  premaxillary 
bones.  The  tusks  have  enamel  over  their  front  and  sides,  like  that  of  a 
rodent,  and  they  grow  from  a  persistent  pulp.  In  the  female,  the}-  do 
not  grow  from  persistent  pulps,  and  do  not  project  beyond  the  jaw. 
Enamel  ensheathes  the  whole  surface  of  the  teeth. 


330  MAMMALIAN  DENTITIONS 

The  sloping  surface  of  each  half  of  the  mandible  is  covered  with  a 
horny  plate,  which  encloses  eight  or  ten  rudimentary  functionless 
teeth,  which  soon  become  shed,  or  absorbed,  and  the  plates  are  covered 
with  stiff  bristles,  and  are  the  analogues  of  whalebone.  Posterior  to 
the  plates,  there  are  four  or  five  degenerated  molars.  These  are  com- 
posed of  vaso-dentine,  having  externally  a  thick  layer  of  cementum. 

Fig.  308 


Skull  of  a  young  Dugong  {Halicore  dugong).     X  5.     Two  pairs  of  molars  only  are  developed. 


The  Rhytina  is  a  genus  which  has  recently  become  extinct.  It 
disappeared  finally  in  1768,  because  it  could  not  defend  itself  when 
attacked,  and  because  it  knew  of  no  method  by  which  it  could  conceal 
itself  from  its  great  and  powerful  enemy — Man.  Behring,  the  dis- 
coverer of  Behring's  Island,  on  which  he  was  wrecked,  was  responsible 
for  slaying  the  rhytina,  for  the  purposes  of  food,  and  incidentally 
caused  the  complete  extinction  of  this  mammal. 


UNGULATA  331 

ORDER  IV.     UNGULATA  {Unguis — a  nail,  or  «»g///a— a  hoof) 

This  Order  comprises  those  terrestrial  mammals  which  possess  hoofs 
rather  than  claws  or  nails,  being  chiefly  vegetarian  and  exhibiting 
mainly  a  herbivorous  type  of  dentition.  The  teeth  are  more  or  less 
bunodont,  with  a  great  tendency  to  a  lophodont  type.  It  is  a  most 
extensive  Order,  embracing  such  creatures,  apparently  very  dissimilar 
in  form,  size,  and  build,  as  the  hyrax  (the  Biblical  coney),  the  elephant, 
the  horse,  the  rhinoceros,  the  pig,  the  antelope,  etc.  The  existing 
members  of  the  Order  are  all  characterized  by  having  toes  enclosed 
either  in  hoofs  or  supplied  with  flat,  broad  nails.  The  elephant  possesses 
five  toes,  the  pig  four,  the  rhinoceros  three,  the  camel  two,  the  horse 
one,  on  each  foot.  In  the  carpus  the  scaphoid  and  lunar  bones  are 
separate;  no  clavicles  exist:  the  mandibular  condyle  is  elongated 
transversely.  The  typical  number  of  cheek  teeth  is  seven,  but  when 
reduced,  the  premolars  have  disappeared,  leaving  the  constant  number 
of  three  pairs  of  molars  in  each  jaw.  Their  surfaces  are  roughened  by 
infoldings  of  the  enamel  from  their  superior  and  lateral  aspects,  and 
the  complex  patterns  make  them  admirable  for  grinding  food-like 
roots,  leaves,  grass,  etc. 

The  ungulates  comprise  the  following: 

Sub-order       I.    {Condylarthra) ,  extinct 
Sub-order     II.   (Ambylypoda),  extinct 
Sub-order  III.   (Anaglopoda) ,  extinct 
Sub-order    IV.   {Typotheria),  extinct 
Sub-order     V.   (Toxodontia),  extinct 
Sub-order  YL  Proboscidea 

Existing  Families 

Elephantidce 

{Dinotheriidce) ,  extinct  (Elephants) 

Procavia,  or  Hyrax 

Eqiiidce  (Horses) 

TapiridcB  (Tapirs) 

RhinocerotidcB  (Rhinoceroses) 


332  MAMMALIAN  DENTITIONS 

Sub-order    VII.  Hyracoidea 
Sub-order  VIII.  Perissodactyla 
Sub-order      IX.    {Litopterna) ,  extinct 
Sub-order       X.  Artiodactyla 

Group  I.  Siiina 

Family      Hippopotamidce 

SuidcB  (Pigs,  etc.) 

Group  II.  Ruminantia 

Family      Tragulina    (Chevrotains) 

Tylopoda       (Camels,  llamas) 
Pecora  (Deer,      antelopes,     oxen, 

giraffe,  goats,  sheep,  etc.) 

General  and  Dental  Characteristics. — Proboscideans^  are  "large 
vegetable-eating  animals,  usually  scantily  covered  with  hair,  and 
with  the  nostrils  and  upper  lips  drawn  out  into  a  long  proboscis. 
Five  digits  on  both  limbs.  .  .  .  Skull  with  abundant  air  cavities 
in  the  roofing  and  other  bones.  The  incisors  are  developed  into 
long  tusks,  exist  in  the  upper  jaw  alone,  in  the  lower  jaw  alone 
{Dinotherium  giganteum),  or  in  both  jaws.  There  are  no  canines. 
The  molars  are  lophodont.  The  clavicle  is  absent.  The  femur  has 
no  third  trochanter.  The  bones  of  the  carpus  are  serially  arranged 
and  do  not  interlock. 

The  persistently  growing  tusks  which  provide  the  ivory  of  com- 
merce, the  trunk,  and  the  structure  of  the  molars  are  three  great 
distinguishing  characteristics  of  the  elephant. 

Elephants  may  live,  under  favourable  circumstances,  for  'three 
hundred  years  or  more.  It  is  said  that  when  Alexander  the  Great 
conquered  Porus,  the  King  of  Media,  he  captured  a  great  elephant 
that  had  fought  for  the  defeated  ruler,  named  him  Ajax,  dedicated  him 
to  the  sun,  and  placed  upon  him  a  metal  band  inscribed  "Alexander, 
the  son  of  Jupiter,  dedicated  Ajax  to  the  Sun."  The  elephant  was 
found,  alive,  three  hundred  and  fifty  years  later. 

The  molar  teeth  of  the  modern  elephant  are  so  huge  that  the  jaws 
cannot  accommodate  more  than  two,  and  a  portion  of  a  third,  at  one 
and  the  same  time.     These  are  gradually  replaced  by  others,  by  means 


UNGULATA  333 

of  an  oblique  succession,  to  the  number  of  three,  and  during  its  life- 
time twenty-four  molars  alone  are  erupted. 

Each  molar  is  made  up  of  a  number  of  transverse  ridges  consisting 
of  dentine,  bounded  by  enamel,  all  united  together  by  cementum.  The 
number  of  the  plates  varies  greatly.  In  the  Indian  elephant,  while 
the  first  permanent  molar  has  only  four  transverse  plates,  the  greatest 
number  in  any  tooth  may  be  twenty-seven. 

The  Indian  Elephant  is  found  in  India,  Ceylon,  and  Malay.  It  is 
much  used  as  a  beast  of  burden,  but  is  often  very  unreliable.  Tusks 
are  usually  present  in  the  male  sex  onl}-.  They  may  measure  8  feet 
in  length,  have  a  circumference  of  17  inches,  and  weigh  90  or  more 
pounds.  Its  food  consists  of  grass,  rice,  and  foliage.  The  ridges  of 
the  molars  are  narrow  and  set  in  a  parallel  fashion. 

The  African  species  has  larger  ears  than  its  Indian  congener.  It 
can  be  tamed.  Tusks  occur  in  both  sexes,  but  are  relatively  larger  in 
the  female  than  in  the  male.  They  are  not  sexual  adornments  only, 
but  are  used  for  uprooting  tubers  and  roots  for  the  purposes  of  food. 
For  these  operations  the  right  incisor  is  used  more  frequently  than  the 
other,  the  result  being  that  this  tooth  is  somewhat  the  shorter  and 
thinner  of  the  two.  Its  food  being  of  a  softer  character  than  that  of 
the  Indian  species,  the  plates  on  the  surface  of  the  molars  appear  in 
lozenge-shaped  ridges,  of  which  perhaps  only  six  or  se\'en  may  be 
found  in  each. 

The  genus  Ilyrax  consists  of  a  group  of  small  rodent-like  mammals 
known  as  coneys.  Their  molars  are  much  like  those  of  the  Rhinoceros; 
their  incisors  grow  from  persistent  pulps.  According  to  Woodward-" 
the  milk  dentition  is:  I  f  C  I  Prn  ^  X  2  =  30  and  the  permanent  den- 
tition is:    I  i  C  ^  (persistent  deciduous  teeth)   Pm  |  M  I  x  2  =  36. 

The  incisors  are  prismatic,  and  the  enamel  is  tubular. 

The  Perissodactyla  {lhp!a(Tb(; — excessive,  or  odd;  Mztmuz — toe)  are 
odd-toed  ungulates,  and  possess  a  toe  which  corresponds  with  the 
middle  digit  of  the  human  hand  or  foot,  and  is  larger  than  those  on 
either  side.  The  total  number  of  toes  in  the  fore  foot  never  exceeds  four. 
Those  in  the  hind  foot  never  exceed  three.  The  tapirs  of  Malay  and 
Tropical  x-\merica  come  of  a  very  primitive  and  ancient  stock,  and 
have  a  remarkable  geographical  distribution.     The  number  of  teeth 


334 


MAMMALIAN  DENTITIONS 
Fig.  309 


Skull  of  a  hyrax  {Hyrax  capensis).     X 
Fig.  310 


Jaws  of  an  adult  horse,  with  the  external  alveolar  plates  removed  to  show  the  shapes,  sizes,  posi- 
tions, and  roots  of  the  teeth,  and  the  cancellous  nature  of  the  bone  of  their  sockets.  X  f.  The 
fourth  premolars  are  generally  somewhat  larger  teeth  than  the  molars.  The  first  premolars  had, 
as  usual,  been  shed  early. 


UNGVLATA 


335 


is  forty-two.^'  The  cheek  teeth  are  bunodont,  the  maxillary  molars 
possess  two  conical  tubercles,  which  are  placed  in  an  antero-posterior 
position.  They  are  united  by  a  ridge  which  forms  the  buccal  wall, 
and,  running  slightly  obliquely  across  the  crown,  are  two  transverse 
crests.     Each  mandibular  molar  has  two  transverse  ridges. 

The  newl}'  born  Brazilian  Tapir  differs  very  considerably  in  colour 
from  its  parents,  its  grey  coat  being  marked  with  stripes  and  spots 
which  disappear  as  it  gets  older.  These  markings  are  particularly 
instructive,  for  they  reveal  the  fact  that  3'oung  animals  more  closely 


Fig.  311 


Skull  of  the  tapir  (Tapir us  iiidicus).      X  A. 

resemble  their  remote  ancestors  than  the  present  day  adults  of  their 
genus.  The  tapir  comes  from  the  same  common  ancestry  as  the  horse, 
and  the  stripes  and  spots  of  the  young  tapir  are  reminders  of  this 
fact,  which  has  been  over  evolved  in  the  stripes  of  the  zebra,  and  the 
spots  often  seen  in  the  coat  of  a  well-groomed  horse.  While  the  latter 
has  been  modified  into  the  form  which  is  so  familiar,  and  another  line 
of  descendants  has  evolved  into  the  equally  dissimilar  rhinoceros,  the 
original  tapir  form,  as  shown  by  fossil  remains,  has  continued  unaltered 
through  many  ages.     Hence  this  grouping  of  the  perissodactjles. 


336 


MAMMALIAN  DENTITIONS 


The  Horse  family  presents  evidences  of  descent  from  a  four-toed 
ancestor  (Orohippus — ofo: — a  limit;  ?~~oc — horse)  and  the  three- 
toed  Protoliippus,  by  the  occurrence  of  the  so-called  "splint  bone," 
which  corresponds  to  the  metacarpals  and  metatarsals  of  the  second 
and  fourth  digits  of  the  typical  five-toed  foot.  The  premolars  and 
molars  consist  of  tall  (hypsodont)  quadrangular  bodies,  with  the 
enamel  thrown  into  a  complex  pattern  of  deep  plications,  the  inter- 
vening flutings  being  filled  with  cementum. 

Fig.  312 


Skull  of  an  African  rhinoceros.  X  tV-  Iii  this  example  there  are  three  pairs  of  molars  and  three 
pairs  of  premolars  only.  The  Indian  species  possesses  a  pair  of  incisors  which  are  used  for  combative 
purposes. 

The  young  horse  has  the  typical  mammalian  dentition.  The 
incisors  have  the  summits  of  their  coronal  portions  deeply  involuted 
like  the  finger  of  a  glove  of  which  the  tip  has  been  pressed  inwards. 
The  age  of  the  animal  can  be  approximately  computed  by  the  depth, 
or  otherwise  (produced  by  attrition)  of  the  cutting  surface,  including 
the  cavity,  the  wearing  down  being  occasioned  by  the  constant  biting 
of  the  teeth  edge  to  edge.  The  canines  occupy  the  centre  of  an  extended 
interval  {diastema)  between  the  incisors  and  premolars;  they  are 
rudimentary   organs   in   the   mare.      Both   maxillary   and   mandibular 


ARTIODACrVLA 


337 


premolars  number  generally  eight  on  each  side  of  the  jaw,  though  the 
anterior  member  of  the  series  is  frequently  lost  at  an  early  age;  they 
have  as  complicated  a  pattern  as  the  molars,  and  are  remarkable,  in 
that  they  are  usually  as  large,  if  not  actually  larger,  than  the  last- 
named  teeth  themselves. 

Fig.  313 


A  B  C 

Teeth  of  {A)  tapir;  (B)  rhinoceros,  and  (C)  horse;  to  show  relative  sizes  of  crowns. 

The  Rhinoceros  \s  distinguished  from  the  tapir  and  the  horse  by 
having,  in  modern  species,  forty-two  teeth.  The  upper  molars  differ 
also  morphologically,  inasmuch  as  their  buccal  surfaces  form  con- 
tinuous walls  undivided  into  lobes.  Their  morsal  surfaces  consist, 
primarily,  of  two  pairs  of  oblique  transverse  ridges,  which  are  more 
irregular  in  outline  than  obtains  in  the  tapir.  The  corresponding 
ridges  in  the  mandibular  series  assume  the  form  of  crescents  instead 
of  simple  transverse  crests. 


ARTIODACTYLA    {drnco; — even;  UxvAoz — toe) 

General  and  Dental  Characteristics. — The  Hippopotamus  is  confined 
to  Africa.  It  constitutes  the  most  primitive  and  least  specialized  type 
of  the  existing  members  of  this  group.  The  cylindrical  incisors  are 
persistently  growing.  In  the  maxilla  they  curve  in  a  downward 
direction;  in  the  mandibles  they  project  forwards.  The  canines  also 
grow  continuously,  those  in  the  upper  jaw  being  directed  downwards. 
The  molars  are  tuberculated,  possessing  four  tri-lobed  cusps,  each 
separated  by  a  deep  longitudinal  and  transverse  groove.  They  undergo 
some  attrition,  as  the  hippopotamus  feeds  on  aquatic  plants  with  which 


338 


MAMAIALIAN  DENTITIONS 


much  sand  is  intermingled.  At  first,  the  wearing  down  of  the  surfaces 
produces  the  appearance  of  four  trefoils;  later  a  two  four-lobed  pattern 
obtains;  and  lastly,  all  original  mould  is  lost,  the  edges  being  composed 
of  enamel  with  a  large  central  area  of  dentine. 

Pigs,  to  which  the  former  show  general  dental  affinities,  have  the 
following  dental  formula:  I  |  C  y   Pm  |  M  |  X  2  =  40. 

Fig.  314 


Skull  of  a  wild  boar  {Sus  scrofa).     X  3. 

Of  the  maxillary  incisors  the  two  median  teeth  are  placed  in  the 
jaw  in  such  a  way  that,  widely  divergent  at  their  base,  the  cutting 
edges,  which  are  not  at  all  trenchant  in  character,  become  approxi- 
mated very  closely  to  one  another;  and  the  outermost  teeth,  separated 
from  the  others  by  a  short  gap,  are  usually  smaller  in  size  and  general 
features.  The  straight  mandibular  incisors  are  procumbent,  and  have, 
in  young  specimens,  on  their  superior  surfaces,  very  marked  longi- 
tudinal ridges  of  enamel. 

In  the  male  the  canines  are  sexual  teeth,  being  larger  than  in  the 
female.  Domestication  has  probably  reduced  their  magnitude,  because 
those  of  the  wild  boar  are  much  greater  than  those  of  the  ordinary 
familiar  pig.  If  a  young  pig  is  deprived  of  the  powers  of  generation, 
through  excision  of  the  testes,  the  huge  development  of  the  tusks  is 
interrupted  and  arrested.     The  upper  canine,  throughout  its  length. 


ARTIODACTYLA 


339 


is  curved  into  the  form  of  a  semi-circle,  though  the  direction  of  its 
socket  is  horizontal  with  the  body  of  the  jaw.  Thin  bands  of  thickened 
enamel  are  found  on  its  lower  and  external  surfaces,  to  withstand  the 
wear  occasioned  by  the  use  of  the  lower  canine.     This  is  a  prismatic 


Fig.  315 


Jaws  of  a  wild  boar  {Siis  scrofa)  placed  side  by  side  to  show  their  relative  shapes,  lengths,  and 
widths.  X  3.  The  molars  increase  in  size  from  before  backwards,  the  third  being  a  long,  narrow 
composite  tooth.     C/.  Fig.  312. 

tooth,  less  pronounced  in  form  than  the  corresponding  maxillar\' 
organ,  and  its  posterior  internal  surface  is  devoid  of  a  covering  of 
enamel. 

In  the  Sus  babirussa  the   maxillary  tusks  become  inclined  upwards 
before  they  leave  the  body  of  the  jaw,  and  appear  as  if  they  arose 


340  MAMMALIAN  DENTITIONS 

from  its  dorsal  surface.  The  older  writers  believed  that,  by  means  of 
these  enormously  curved  teeth,  the  animal  could,  and  did,  sometimes, 
suspend  itself  from  the  branches  of  trees.     (Beddard.) 

The  cheek  teeth  increase  in  size  from  before  backwards.  The  first 
is  a  small  wedge-shaped,  bi-rooted  tooth,  the  first  premolar  of  some 
writers,  but  perhaps  a  deciduous  molar  i^"  the  fourth  premolar  is  brachyo- 
dont,  bi-tuberculate,  and  quadruple  rooted.  The  first  molar  possesses 
four  cusps  divided  by  a  cruciform  sulcus,  the  cingulum  is  elevated  into 
a  posterior  transverse  ridge;  the  cusps  of  the  second  molar  present 
small  accessory  tubercles  and  the  posterior  transverse  ridge  is  pro- 
nounced, being  still  more  highly  developed  in  the  third  member  of  the 
series,  while  the  tooth  itself  is  almost  twice  the  length,  in  the  mesio- 
distal  diameter  of  its  immediate  neighbour. 

The  DicotylidcB — the  Peccaries — the  small  American  swine,  have  the 
extremities  of  their  maxillary  tusks  directed  downwards  in  the  ordinary 
way,  the  posterior  edges  being  narrow  and  sharp.  The  total  dental 
armament  numbers  thirty-eight  members. 

Selenodont  teeth  are  found  in  the  Camels,  Llamas,  Oxen,  etc.  All 
animals  possessing  these  are  ruminants,  that  is,  they  chew  the  "cud," 
an  Anglo-Saxon  derivative  which  is  applied  to  the  re-chewed  food 
regurgitated  into  the  mouth  from  the  first  stomach.  In  the  camels,  all 
premolars  and  molars  are  selenodont,  and  therefore  non-tuberculated. 
The  formula  here  is:    I  i  C  1  Pm  I  M  -f  X  2  =  34. 

The  males  of  the  Chevrotains,  hornless  deerlets,  or  mouse-deer,  have 
well-developed  maxillary  canines  which  are  said  to  be  used  for  sus- 
pensory purposes.    The  formula  is:  If  C  I  Pm  |  M  |  X  2  =  34. 

They  differ  from  camels  in  the  absence  of  maxillary  incisors,  and  in 
the  lower  jaw  the  canines  are  approximated  to  the  incisors.  They 
form  the  oldest  type  of  Selenodontia,  and  are  oriental  and  West  African 
in  range.  The  tusks  of  the  males  of  the  species  Tragidus  must  not  be 
confused  with  those  of  the  Moschus  moschiferus — the  musk-deer. 

CervidcB.  The  deer  tribe  is  one  of  four  families  which  constitute  the 
Pecora  or  true  ruminants.  Like  the  camels  and  chevrotains  they  chew 
the  "cud,"  and  closely  agree  with  the  latter,  in  that  the  maxillary 
incisors  are  entirely  absent,  their  place  being  occupied  by  a  fibrous 
pad  covered  with  thick  oral  epithelium.     The  lower  canine  assumes 


ARTIODACTYLA 


341 


an  incisiform  character,  and  is  placed  close  to  the  distal  surface  of 

the  third  incisor. 

Fig.  316 


Skull  of  a  chevrotain  {Tragulus  meminna) .     X  |.     Both  sexes  are  hornless,  and  both  possess 
well-developed  maxillary  canines. 

Deer  are  never  found  in  Africa  south  of  the  Sahara,  nor  in  Mada- 
gascar. Their  heads  are  ornamented  with  antlers — branched  deciduous 
appendages  incorrectly  termed  "horns,"  which  grow  from  the  frontal 
bone. 

Fig.  317 


Skull  of  a  male  Chinese  water  deer  i^IIydropotcs  nicnnis).     X  f.     Cf.  Fig.  24  and  Fig.  316. 

The  more  typical  varieties  are  Muntjacs  of  India,  China,  and 
Eastern  Thibet,  the  male  being  distinguished  by  large  maxillary  canines; 
and  closely  allied  are  other  small  deer  from  the  same  localities,  viz., 
the  genus  Elaphodus,  "tufted  deer,"  the  males  of  which  have  large 
upper  canines.  The  genus  Cervus  includes  red  deer  and  fallow-deer, 
and   is  confined   to   the   Old   World   except   the   magnificent   Wapiti. 


342 


MAMMALIAN  DENTITIONS 


Rudimentary  canines  exist  in  the  jaws  of  many  deer,  but  it  is  clear  that 
the  common  fallow-deer  of  the  British  parks,  the  roe-deer,  and  the 
Persian  fallow-deer  have  none.  The  Hydropotes  inermis,  inhabiting 
the  islands  of  the  Yang-tse-kiang,  is  an  aberrant  antlerless  member  of 
the  last  family,  and  resembles  the  musk-deer  in  the  remarkable  length 
and  strength  of  its  maxillary  canines. 

Other  members  of  the  CervidcB  are  the  reindeer,  and  the  elk  or 
moose,  the  largest  representative  of  all  living  deer,  whose  dental 
characteristics  conform  to  the  usual  type. 


Fig.  318 


Skull  of  a  camel  (Camelus  dromedarius).      X 


It  is  thus  obvious  that  maxillary  canines  are  generally  absent  in  the 
deer,  and  are  present  in  the  musk  deer,  the  Muntjac,  the  goat-like 
Chinese  water  deer,  and  the  tufted  deer. 

The  Giraffe  (Arabic  zaraf — "one  who  walks  quickly")  is  indigenous 
to  Africa,  its  long  neck  consisting  only  of  seven  vertebrae,  as  in  the 
dissimilar  hippopotamus,  serves  as  a  watch-tower,  like  that  of  the 
ostrich,  which  lives  under  like  conditions.  There  are  no  maxillary 
incisors  or  canines;  the  premolars  are  brachyodont,  a  characteristic 
feature  in  the  mandible  being  the  length  of  the  diastema — between 
the  incisors  and  canines.  The  gregarious  Pronghorn  of  Eastern,  Central, 
and  North  America  is  regarded  as  a  distinct  family,  from  the  fact  that 


EDENTATA  343 

not  only  are  the  sheaths  of  the  antlers  branched,  but  that  they  are 
annually  shed,  and  their  place  taken  by  new  "velvet"  which  has  been 
growing  up  beneath  the  old  ones.  The  dentition  requires  no  special 
description. 

The  largest  group  of  the  artio-dactyle  ungulates  is  that  of  the  hollow- 
horned  ruminants  or  Bovidce.  The  horns  are  unbranched,  are  com- 
posed of  an  underlying  core  of  osseous  material  springing  from  the 
frontal  bone,  and  are  covered  with  a  hollow  horny  sheath  which  is 
never  shed.     Hence  the  difiference  from  antlers. 

Some  are  possessed  of  maxillary  canines.  Antelopes,  the  least 
specialized  group,  have  a  hypsodont  type  of  dentition.  Broad,  square, 
maxillary  molars  are  found  in  the  African  duikerboks  [Cephalophus) ; 
narrow  maxillary  molars  in  the  African  Antelope,  the  elegant  Gazelle, 
the  Sheep,  etc.  In  the  Ox,  Sable  antelopes,  Buffaloes,  and  Bisons  the 
maxillary  molars  are  tall,  broad,  and  quadrilateral,  and  on  the  lingual 
side,  a  narrow,  but  well-defined  accessory  column  is  added  to  the 
four  large  normal  crescentic  ones.  In  the  Kudus  the  broad,  square 
crown  may  be  either  hypsodont  or  brachyodont. 

Sheep,  Goats,  Chamois,  and  Musk-ox  are  markedlj^  hypsodont,  the 
upper  molars  having  only  four  crescentic  columns. 


ORDER    III.    GANODONTA   (Wortman) 
Extinct 


ORDER  II.     EDENTATA  {E  or  e.v—without;  dentes—te&th) 

The  Edentates  are  "terrestrial,  partly  subterranean,  or  arboreal 
creatures  of  quite  small  to  gigantic  size  (some  extinct  genera)  with 
frequently  a  covering  of  scales  or  bony  scutes.  Limbs  clawed.  Teeth 
either  totally  absent,  or,  if  present,  imperfect  in  structure,  being 
without  enamel,  and  not  forming  a  complete  series,  incisors  and 
canines,  as  a  rule,  being  absent."      (Beddard.) 

The  Order  contains  the  Sloths,  Ant-bears,  Anuadillos,  Main's,  and 
Orycteropus  (Cape  Ant-eater  or  Aard-vark). 

The  term  applied  to  this  Order  is  only  partiall}-  correct,  as  many 


344  MAMMALIAN  DENTITIONS 

members  possess  teeth;  though  enamel  organs  have  probably  existed 
in  foetal  conditions.^  ^^  " 

One  genus,  Armadillo,  has  functional  milk  teeth. 

Sub-order  I  Family 

Xenartha  {Eivo:^  unusual; 

dpdpo'j,  joint)  Myrmecophagidce  (Great  ant-eaters) 

Bradypodidce  (Sloths) 

DasypodidcB  (Armadillos) 

MylodontidcB,  extinct 
Megalomychidce,  extinct 
MegatheriidcB,  extinct 

Sub-order  II  Family 

Nomarthra  (Nop/xoi,  usual; 

dfjdpou^  joint)  Orycteropodidce  (Aard-varks) 

Group 

ManidcB  (Pangolins) 

General  and  Dental  Characteristics. — The  South  American  Great 
Ant-eaters  are  all  anodontous. 

The  arboreal  Sloths  live  in  the  forests  of  Tropical  America.  They 
possess  no  tails.  Their  movements  are  exceedingly  slow,  but  they 
can  conveniently  escape  the  notice  of  their  enemies  by  being  difificult 
to  distinguish  from  the  twigs  and  leaves  of  the  branches  of  the  trees 
to  which  they  cling.  The  hair  is  long  and  shaggy,  and  from  the 
presence  of  adventitious  green  algae  gives  the  animal  the  appearance  of 
a  lichen-covered  bough.  Nature  in  the  sloths  is  very  imperfect,  in 
spite  of  their  excellent  organization  and  habits  with  regard  to  their 
particular  environments. 

The  teeth  are  almost  C3-lindrical  in  section,  rootless,  and  periodically 
growing,  ten  in  the  maxillae  and  eight  in  the  mandible,  and  are  com- 
posed of  vaso-dentine.    Sloths  are  monophyodont  and  homodont. 

The  unique  Armadillos  frequently  present  a  large  number  of  teeth, 
sometimes  as  many  as  forty  in  each  jaw.  Generally  speaking,  however, 
the  number  is  seven,  eight,  or  nine  in  each  half  of  the  jaw,  one  being 


EDENTATA 


345 


implanted  in  the  premaxillary  bone.     The  teeth  resemble  those  of  the 
sloth. 

In  Bradypus  the  teeth  are  small,  of  equal  size,  and  being  placed 
opposite  each  other  in  the  dental  arches  are  permanently  worn  down 
flat.      In  CholcepHS  the  anterior  tooth  in   each  jaw  is  caniniform  and 

twice  as  long  as  the  others. 

Fig.  319 


Skull  of  a  two-toed  sloth  (Cholospus).     X  -.    The  first  pair  of  teeth  in  each  jaw  are  longer  and 
more  tusk-like  than  the  others.     Cf.  Fig.  58. 

The  Aard-varks,  or  Earth  pigs  of  South  Africa,  are  diplyodonts. 
According  to  Oldfield  Thomas^^  there  are  seven  deciduuos  teeth  in 
each  maxilla — none  in  the  premaxillae;  and  in  the  mandible  only  four 
milk  teeth  in  each  half.  The  permanent  series  includes  five  premolars 
and  molars  in  each  half  of  each  jaw,  the  latter  being  differentiated 
from  the  former  in  the  presence  of  a  median  furrow  which  divides 
them  into  halves.  They  consist  entirely  of  plicidentine;  hence  are 
similar  histologically  to  those  of  Myliobates. 

The  Pangolins  being  ant-eaters,  are,  like  the  great  ant-eaters,  eden- 
tulous, though  traces  of  a  vestigial  dentition  can  be  found. ^^  ^^  ^*  On 
occasion,  they  capture  their  food  by  erecting  their  scales  and  feigning 
death.  Ants  creep  between  these  erected  scales,  which  are  then  closed 
and  the  creatures  carry  their  food  to  a  stream,  where  they  become 
submerged,  and  on  liberating,  the  ants  swim  about  and  are  speedily 
devoured  by  their  temporary  hosts. 


346  MAMMALIAN  DENTITIONS 


ORDER  I.      MARSUPIALIA   {Marsupium — a  pouch) 

The  Marsupials  differ  from  the  preceding  orders  of  mammalia 
chiefly  from  the  point  of  view  of  the  absence  of  placentae.  During 
intra-uterine  life,  the  foetal  communicate  directly  with  the  maternal 
blood  vessels  by  means  of  the  placenta,  an  arrangement  which  ensures 
a  more  or  less  highl}'  developed  state  at  birth.  In  this  group,  however, 
there  is  no  direct  communication  between  the  circulatory  systems  of 
parent  and  offspring;  hence  the  imperfect  state  of  development  of 
the  young  at  birth.  They  are  called  Implacental  mammals,  and 
structurally  occupy  a  position  in  Nature  between  the  Prototheria  or 
Monotremes,  and  the  more  typical  Eutheria,  which  they  more  closely 
resemble. 

They  may  be  defined  as  follows:  "Terrestial,  arboreal  or  burrowing 
(rarely  aquatic)  mammals,  with  furry  integuments,  palate  generally 
somewhat  imperfectly  ossified;  angle  of  lower  jaw  nearly  always 
inflected.  The  clavicle  is  developed.  Arising  from  the  pubes  are 
well-developed  and  ossified  epipubic  bones.  .  .  .  Teeth  often 
exceed  the  typical  Eutherian  number  of  forty-four;  molars  generally 
four  on  each  side  of  each  jaw.  As  a  rule  but  one  tooth  of  the  milk  set 
functional,  which  is  (according  to  man^O  the  fourth  premolar. 

Many  authorities  regard  the  teeth  as  belonging  to  the  deciduous 
dentition.  Elsewhere  it  has  been  pointed  out,  however,  that  they 
probably  really  belong  to  the  permanent  series,  and  that  the  last 
premolar  which  gets  shed  is  actually  one  of  the  permanent  series 
Avhich,  through  kinking  of  the  tooth-band,  has  been  extruded  by 
another  tooth  beneath.  The  polyprotodonts  only  have  a  greater 
number  of  teeth  than  forty-four,  and  the  feeble  development  of  their 
marsupia  indicates  that  they  are  the  most  primitive  type  of  marsupial. 
Tubular  enamel  exists  in  the  Wombat.^" 

Marsupials  are  now  confined  to  the  Neogaeic  realm,  which  comprises 
the  Australian  continent,  Papua,  Celebes,  South  and  Central  America. 
They  are  of  very  ancient  lineage.  In  Mesozoic  times  they  existed  in 
North  America  and  in  Europe.  In  the  former  they  persist  to  the 
present  day,  being  represented  by  the  opossums.     In  the  latter  they 


MARSUPIALIA 


347 


became  extinct  during  the  Tertiary  period.  Diprotodonts  exist  in 
both  America  and  AustraHa,  a  fact  which  may  be  explained  by  the 
hypothesis  that  there  was  formerly  a  land-connexion  in  the  Antarctic 
hemisphere  along  which  the  Australian  diprotodonts  migrated  into 
South  America. 


Sub-order  I 

Diprotodontia"^  (-I'-Jo — two ; 
7:pozs(joz — in  front; 
dooui; — tooth) 


Family 

A.  Macropodidce  (Kangaroos,  wallabies,  rat- 
kangaroos,  etc.) 

Sub-family  i.  Macropodidce    (Kangaroos, 

wallabies) 
Sub-family  2.  PotoroincE  (Rat-kangaroos) 
Sub-family  3.  Hypsipryrmwdontidce 
(Musk  kangaroos) 

B.  Phalangeridce  (Phalangers) 
Sub-family  i.  Phalangerince  (Cuscus) 
Sub-family  2.  Phascolarctince  (Koalas) 
Sub-family  3.  Phascolomyince  (Wombats) 
Sub-family  4.   Tarsipedince  (Tarsipes) 

C.  EpanorthidcB — Ccenolestes 


Sub-order  II 

Polyprotodontia]  (jto'/jj:; — 
many;  TipozsjioQ — in  front; 

ddou:; — tOOth) 


Fa  mily 

Dasyuridce  (Thylacines,  Sarcophilus, 

"Native  cats") 
Didelphydce  (Virginian  opossums) 
Peramelidce.  (Bandicoots) 
Notoryctidce  (Australian  marsupial  moles) 


General  Dental  Characteristics. — The  Diprotodonts  are  character- 
ized by  the  number  of  the  incisors  of  which  there  are  never  more  than 
two  in  the  lower  and  six  in  the  upper  jaw.  The  first  are  alwa^'s  large, 
having  sharp  cutting  edges.  The  maxillary  canines,  if  present,  are 
small;  in  the  mandible  they  are  absent.  The  four  pairs  of  molars 
possess    broad    quadrangular    crowns,    and    have    either    four    blunt, 


*  This  term  refers  to  the  mandibular  incisors  only, 
t  This  term  refers  to  the  lower  jaw  only. 


348  MAMMALIAN  DENTITIONS 

rounded  tubercles  or  a  pair  of  transverse  ridges  on  their  surfaces — a 
type  of  dentition  admirably  adapted  to  a  vegetable  dietary. 

Kangaroos  vary  in  size  from  that  of  a  rabbit  to  that  of  a  human 
being,  and  are  specially  noted  from  the  possession  of  rooted  teeth.  The 
upper  incisors  are  placed  almost  vertically.  The  lower  project  hori- 
zontally forwards.  Owing  to  the  laxity  of  the  fibrous  tissue  which 
joins  the  two  halves  of  the  lower  jaw,  these  latter  are  capable  of  under- 
going movements  like  the  working  together  of  the  blades  of  a  pair  of 
scissors. 

Fig.  320 


Jaws  of  a  kangaroo  {Macropus  rufiis).     X  j\.    The  jaws  are  placed  side  by  side  to  show  their 
relative  proportions. 


The  formula  is:    If  C|  Pm  i  M  f  x  2  =  28. 

Older  animals  possess:  I  f  C  I  Pm  f  M|X2=  16. 

The  upper  incisors  are  rooted,  the  lower  incisors  are  continuously 
growing. 

In  the  Hypsiprimniis  (Rat  Kangaroo)  of  North  Queensland  the 
only  premolar  is  exceedingly  long  and  blade-like,  with  a  narrow  tren- 
chant edge.  It  displaces  two  teeth,  viz.,  a  tooth  which  is  the  one 
deciduous  molar  of  some  authors  (dm'*)  or  the  premolar  of  others,  and 
also  a  premolar  (Pm-). 

The  teeth  are  variable  in  form  and  number  in  the  Phalangers,  the 


MARSUPIALIA 


349 


canines  are  feeble,  and  a  space  divides  the  incisors  from  the  molars. 
The  number  of  teeth  ranges  from  twenty-eight  to  forty,  owing  to  the 
frequent  presence  of  a  number  of  small  functionless  anterior  organs. 

As  a  general  rule,  the  formula  is:  I  f  C  -^  Pm  \^^  M  f  x  2  =  32  or  36. 

They  differ  from  kangaroos  in  the  absence  of  the  deep  pocket-like 
pit,  characteristic  of  that  genus,  on  the  outer  side  of  the  posterior 
portion  of  the  mandible,  and  the  lower  incisors  are  not  so  freely  mov- 
able on  one  another.  All  the  phalangers  are  arboreal  and  of  nocturnal 
habit.  Most  are  provided  with  prehensile  tails,  few  possess  patagia, 
to  enable  them,  like  the  flying  lemur,  to  leap  from  tree  to  tree.  The 
majority  are  vegetable  feeders;  some  are,  however,  insectivorous  and 
some  carnivorous. 

J~IG.  321 


Skull  of  a  koala  {Phascolarctus  cinereus) 


The  solitary  Koala  of  Eastern  Australia  somewhat  resembles  a 
small  bear.  It  is  tailless,  has  short,  broad,  dental  arches,  and  large 
teeth.     Its  dentition  is:  I  f  C  i  Pm  i  M  t  X  2  =  36. 

Three  species  of  Wombat,  one  of  which  is  confined  to  Tasmania," 
the  others  to  Australia,  South  of  the  Tropic  of  Capricorn,  are  burrowing, 
rodent-like  animals  with  the  formula  of:  I  y  C  {f  Pm  t  ^I  4  X  4  =  24. 

This  aberrant  type  differs  from  its  congeners  in  that  it  is  diphyo- 
dont.i^  Its  dentition  is  rodent-like,  all  the  teeth,  including  the  molars, 
are  persistently  growing;  cementum  is  found  superficially,  and  the 
enamel  is  non-tubular. 


350 


MAMMALIAN  DENTITIONS 


Tarsipes,  three  inches  in  length,  an  insect  and  honey  eater,  has 
upper  canines,  fairly  well-developed  lower  incisors,  a  single  pair  of 
maxillary  premolars,  and  only  three  pairs  of  molars  in  each  jaw.  There 
is  no  inflexion  of  the  angle  of  the  mandible. 


Fig. 


Skull  of  the  Dingo  of  Australia  i^Canis  dingo) 


Amongst  the  Polyprotodonts,  Dasyures  are  carnivorous  marsupials. 
They  inhabit  Australia,  Tasmania,  New  Guinea,  and  many  adjacent 
islands.  There  are  eight  incisors  in  the  upper  and  six  in  the  lower  jaw. 
The  molars  have  multicuspidate  crowns. ^^ 

The  Thylacine,  or  Tasmanian  wolf,  a  dog-like  creature,  has  the  fol- 
lowing formula :  I  t  C  y  Pm  |  M  t  X  2  =  46. 

Sarcophiliis  differs  in  the  fact  that  two  pairs  of  premolars  only 
are  present  in  each  jaw.  The  maxillary  molars  (except  the  fourth)  are 
short,  wide,  triangular,  and  strong.  Dasyures  have  teeth  which  are 
numerically  similar  to  Sarcophilus,  but  they  are  not  so  well  developed. 

Opossums  are  distinguished  from  the  last  Family  by  having  eight 
lower  and  ten  upper  incisors — fifty  teeth  in  all." 

The  dental  formulas  of  the  Bandicoot  is:  I  |  C  |  Pm  |  M  t  X  2  =  48. 

The  incisors  are  relatively  small  in  size;  the  canines  are  tusk-like; 
the  molars  are  multituberculate  and  very  sharp.'" 

An  aberrant  type  is  seen  in  Myrmecobius ,  or  banded  ant-eater,  which 
is  very  remarkable  in  its  numerical  variations  of  the  teeth,  of  which 
the  following  is  the  formula:  I  |  C  x  Pm  |  M  f  X  2  =  54. 


PROTOTIIERIA 


351 


The  molars  are  separated  from  one  another  by  intervals;  the  inner 
cusps  of  the  lower  teeth  being  larger  than  the  outer  ones.  Four  pairs 
of  mandibular  incisors  may,  at  times,  be  developed. 


Skull  of  an  opossum  (Didelphys  virginiana).      X 
Fig. 324 


Skull  of  a  bandicoot  (Perameles). 


The  marsupial  mole  ( Notoryctes  typhlops)  lives  by  burrowing  in 
the  sand  of  the  deserts  of  Australia  in  search  of  insect  food.  This 
admixture  of  sand  with  the  soft-bodied  insects  produces  much  attri- 
tion of  the  teeth.  The  animal  is  of  a  pale  golden-red  colour,  and  must 
be  distinguished  from  Chryschloris,  or  Golden  Mole.  It  measures  in 
vertex-breach  diameter  about  five  inches.  The  maxillary  molars 
have  triangular  crowns  and  carry  three  cusps  only. 


Sub-class  I.     Prototheria 

Contrary  to  the  initiation  of  Professor  Huxley,  modern  zoologists 
divide  Mammals  into  two  primary  classifications,  vis.:  (A)  Prototheria 
and  (B)  Eutheria. 

The  preceding  pages  have  dealt  with  the  main  features  of  the  latter; 
it  now  remains  briefly  to  describe  the  dental  features  of  those  creatures 
which  stand  at  the  base  of  the  Mammalian  series,  and  are  the  lowest 
in  the  scale  of  animals. 


352 


MAMMALIAN  DENTITIONS 


The  order  Monotremata  {Mom; — single;  Trjyj/JM — aperture)  include  the 
Ornithorhynchus  (Duck-billed  platypus)  and  Echidna. 

They  may  be  defined  as  "Mammalia  with  no  teats  but  with  a 
temporary  pouch  in  which  the  young  are  hatched,  or  to  which  they 
are  transferred  after  hatching,  and  into  which  open  the  ducts  of  the 
mammary  glands.  .  .  .  Mammary  glands  of  the  sudoriparous 
and  not  the  sebaceous  type  of  epidermic  gland.  Oviparous,  with  a 
large-yolked  and  meroblastic  ovum,  enclosed  within  a  follicle  of  two 
rows  of  cells.  "^ 

Fig.  325 


Jaws  of  a  duck-billed  platypus  {Ornithorhynchus.)     X  f.     The  jaws  are  placed  side  by  side 
to  show  their  relative  proportions. 

The  most  salient  feature  of  the  group  is  that  the  "eggs  are  large- 
yolked  and  develop,  so  far  as  regards  their  early  stages,  therefore, 
after  the  fashion  of  the  egg  of  a  reptile." 

There  are  some  existing  Families  of  these  archaic  creatures,  {i)  the 
Echidnidcz,  and  {ii)  the  Ornithorhynchidce. 


PROTOTIIERIA  353 

The  Echidna,  or  Australian  ant-eater,  is  edentulous  and  possesses 
no  corneous  substitutes  for  teeth. 

The  Ornithorhynchus  is  remarkable  from  its  curious  duck-like  bill  or 
"beak,"  which  is  covered  with  a  fine  skin  in  which  many  sensitive 
tactile  nerve  organs  are  situated. 

Prior  to  1888  it  was  believed  to  be  toothless.  Then,  however,  Poul- 
ton^-  discovered  the  presence  of  tooth  germs  in  embryos.  Oldfield 
Thomas^^  has  clearly  shown  that  eight  or  ten  calcified  molars  exist; 
and  he  believes  that  they  persist  during  a  considerable  part  of  the  life 
of  the  animal,  i.  e.,  about  eight  or  nine  months,  during  which  time  it 
is  about  half-grown,*  and  become  shed  after  undergoing  attrition  by 

Fig.  326 


Skull  of  an  echidna,  or  spring  ant-eater.     X  5. 

food  and  sand,  their  places  being  taken  by  horny  plates,  which  are 
developed  from  the  oral  epithelium  growing  around  and  beneath  the 
calcified  teeth.  It  is  probably  this  mode  of  development  of  the  cor- 
neous structures  which  determines  the  loss  of  the  molars.  If  the 
superior  surfaces  of  the  former  be  examined  it  will  be  seen  that  they 
are  grooved  and  hollowed  for  the  implantation  of  the  molars  of  which 
they  form  the  remains  by  the  original  alveolar  sockets. 

The  horny  plates  are  four  in  number  in  each  jaw;  there  are  twelve 
teeth,  eight  large  and  four  very  diminutive.  The  maxillary  series  have 
broad  crowns  with  two  long  lingual  cusps  and  small  accessory  cusps 
along  the  border.  A  reverse  anatomical  condition  obtains  in  the 
mandibular  teeth.  All  have  short  roots.  In  structure  the  enamel  is 
of  a  simple  character  and  the  dentine  is  supplied  with  an  abundance 

*  In  a  private  letter  written  in  the  spring  of  1912,  Mr.  Brooke  NichoUs,  of  Melbourne,  tells  the 
author  that  it  is  his  conviction  that  these  calcified  teeth  are  not  to  be  found  after  the  third  month,  .s- 
23 


354  MAMMALIAN  DENTITIONS 

of  interglobular  spaces,  probably  affording  evidences  of  its  origin  from 
an  earlier  and  completer  form. 

References 

1.  Ballowitz.  "Das  Schmelzorgan  des  Edentaten,  seine  Ausbildung  in  embryo,  und  die  Per- 
sistenz  seines  Keimrandes  bei  dem  erwachsenen  Thier,  "  Archiv.  fiir  microscop.  Anatomie,  1892. 

2.  Bate.    "On  the  Dentition  of  the  Mole,"  Trans.  Odontolog.  Soc.  Great  Britain,  1865. 

3.  Beddard.    "The  Book  of  Whales,  "  1900,  "  Mammalia,  "  Cambridge  Natural  History,  1902. 

4.  Brandt.     "Ueber  der  Zahnformel  der  Spitzmause,  1878. 

5.  Broom.  "Some  Observations  on  the  Dentition  of  Chrysochlovis  and  on  the  Tritubercular 
Theory,  "  Annals  of  Natal  Government  Museum,  1909. 

6.  Elliott.    "Concise  Knowledge  History,  "  1897. 

7.  Hilzheimer.  "Variationen  des  Caniden-gebisses  mit  besondere  Berucksichtingung  des  Haus- 
hundes, "  Zeitschrift  fiir  Morph.  mid  Anthropologic,  1905. 

8.  Huxley.  "On  the  Cranial  and  Dental  Characters  of  the  Canids,  "  Proc.  Zool.  Soc.  of  London, 
1880. 

9.  Kiikenthal.  "Einige  Bemerkungen  iiber  die  Saugethier-bezahnung, "  Anal.  Anzeiger,  1891; 
"Das  Gebiss  von  Didelphys, "  Anal.  Anzeiger,  1891;  " Entwickelungsgeschichte  Untersuchungen 
am  Pinnipediergebisse, "  Jenaische  Zeitschrift  fiir  Natur,  1893. 

10.  Nawroth.    "Zur  Ontogenese  der  Schweine-molaren,"  1893. 

1 1 .  Parker.    ' '  Some  Points  in  the  Anatomy  of  the  Indian  Tapir, ' '  Proc.  Zool.  Soc.  of  London,  1882. 

12.  Poulton.  "The  True  Teeth  and  the  Horny  Plates  of  Ornithorynchus,"  Quart.  Jour.  Micro. 
Science,  1889. 

13.  Rose.  "Beitrage  zur  Zahnentwickelung  der  Edentaten,"  ^Mdi.  Anzeiger,  1892;  "Ueber  die 
Zahnentwickelung  von  Phascolomys  Wombat,"  Sitzungsber.  der  k.  Preuss.  Akad.  d.  Wissensch.  zu 
Berlin,"  1893. 

14.  Sclater,  W.  L.  and  P.  L.    "The  Geography  of  Mammals, "  1899. 

15.  Oldfield,  Thomas.  "On  the  Homologies  and  Succession  of  the  Teeth  in  the  Dasyuridw,  with 
an  Attempt  to  Trace  the  History  of  the  Evolution  of  Mammalian  Teeth  in  General,"  Phil.  Trans. 
London,  1887;  "On  the  Dentition  of  the  Ornithorynchus,"  Phil.  Trans.  London,  1890. 

16.  Marett  Tims.  "On  the  Tooth-genesis  in  the  Canidce,"  Journal  Linnman  Soc.  of  London, 
1896;  "Tooth  Vestiges  and  Associated  Mouth  Parts  in  the  Manidce,"  Journal  Anal,  and  Phys.,  1908. 

17.  Tomes,  Chas.  "On  the  Development  of  Marsupial  and  Other  Tubular  Enamels,"  Phil. 
Trans.  London,  1897;  "A  Manual  of  Dental  Anatomy,"  1898. 

18.  Weber.  "Beitrage  zur  Anatomie  und  Entwickelung  der  genus  Manis,"  Zool.  Ergebnisse 
einer  Reise  im  Niederlandische  Ost-Indien,  1892. 

19.  Wilson,  J.  T.,  and  Hill,  J.  P.  "Observations  on  Tooth  Development  in  Ornithorynchus," 
Quart.  Jour.  Micros.  Science,  1907. 

20.  Woodward,  Martin.  "On  the  Teeth  of  Certain  Inseclivora,"  Proc.  Zool.  Soc.  of  London,  1896; 
"On  the  Milk  Dentition  of  Procavia  (Hyrax)  Capensis,"  Proc.  Zool.  Soc.  of  London,  1892;  "On 
the  Development  of  the  Teeth  in  the  Macropodidce,"  Proc.  Zool.  Soc.  of  London,  1893. 


GLOSSARY 


AcRODONT — axpou^   the    summit — teeth    placed    on    the    top    of    the    jaw,    as    in 

sphenodon  and  eel. 
Aglypha — «,  negative — p^Jtfiz — a  notch  or  groove. 
Alveolus — alvens — a  hollow  vessel  (diminutive  form  of) . 
Basion — basis — the  base. 

BiLOPHODONT — bis,  twice;  /o^''oc — a  ridge — as  in  the  Tapir. 
BR.4CHY0D0NT — j^pay^o; — short. 
Brachycephalic — ?P"-T'Js — short,  xs^l'alrj — head;  skulls  of  which  the  breadth  is  at 

least  four-fifths  of  the  length. 
BuNODONT — i3uuu6:: — a  mound. 
Caniniform — canine-like . 
Cervical — cervis — a  neck. 
Ch^todont — Z«;i"^ — a  mane. 
CiNGULUM — cingulum — a  girdle. 
Coronal — corona — a  crown. 
Cursorial — cursus — running. 
Deciduous — deciduus — falhng  off,  or  shedding. 
DiASTEM.A. — SidaTYj/m — an  interval. 

DiPHYODONT — o;c — double  or  two;  <^''j/-r/ — a  company  or  series. 
DiPROTODONT — oic: — two;  7zri(7jTo; — front. 
Distal — distant. 

Dolichocephalic — oo).ty6; — long;   y.i(/'rA-/j — head;  longheaded  skulls. 
Dents  en  brasses — teeth  collectively  like  brushes. 
Dents  en  cardes — teeth  collectively  like  combs,  whose    antero-posterior  diameter 

exceeds  the  lateral  diameter. 
Dents  en  velours — teeth  collectively  like  velvet. 
Edentata — e,  negative;  dens,  denlis,  a  tooth — edentulous. 
Entoconid — ivroc — within,  inside;  xiovoz — a  cone. 
Ethnic — s^voc — a  nation. 
Eutheria — =-u — ordinary;  H'r/<i — a  wild  beast. 
FossoRiAL — fodio,  fossum,  I  dig — digging  or  burrowing. 
GoMPHOSis — /'"/^i^oc — a  nail. 
GoNiAN — ycoi^io- — an  angle. 

Gymnodont — yupvo!; — naked  or  bare,  as  in  the  Diodon. 
Haplodont — ii-loo^ — simple,  as  in  the  dolphin. 
Heterodont — inpo; — different,  as  in  Man,  pig,  etc. 


356  GLOSSARY 

HoMOODONT-:-o/>!oc — alike,  as  in  the  dolphin,  sloth,  armadillo. 

Hypocone — ^TTo — beneath  or  under;  xwuo^ — a  cone. 

Hypsodont — o(p! — high,  as  in  the  horse,  elephant. 

LoPHODONT — /65A0C — a  ridge,  as  in  the  Tapir. 

Macrodont — iJMXfw^ — large. 

Megadont — «?;-« — very  much.  , 

Mesial — />.iao: — middle . 

Mesodont — /-leaoi; — middle. 

Mesognathotjs — /iio-of — middle;  y'Adu: — jaw. 

Metacone — n^rd — behind,  xcmoz,  a  cone. 

MiCRODONT — fjuxpoz — small. 

MoNOPHYODONT — noijo^ — one;  ^'"j/-^ — a  series  or  company. 

MoRSAL — morsus — a  bite. 

MuLTiTUBERCULAR — multus — many,  tuberculum,  diminutive  of   tuber,  a  knob  or 

cusp. 
Occlude — occluder e — to  close,  to  shut  up. 
Odontogeny — ooo^c — a  tooth;  yswdco — to  produce. 
Opisthoglypha — omadeUj  behind;  p-^ifk — a  notch  or  groove. 
Orthognathous — ofidoz — usual;  yuddo:; — mouth  or  jaw. 
Paracone — -apd — in  front  of;  xoji'O!; — a  cone. 
Patagium — a  parachute. 
Pectinate — pec  ten — a  comb. 
Pleurodont — -Xeijpd — the  side;  as  in  Varanus. 
Polyphyodont — TtokuQ — many ;  if>^j)-'/j — series. 
Prognathism — 71  pb — forward ;  yi'ddo: — jaw. 
Prosthion — -poadiv — in  front. 

Proteroglypha — Tzpnzspo:; — in  front;  Y?.iJ(/'k — a  notch  or  groove. 
Protocone — TLpcijzo:; — first;  xcovoc — a  cone. 
Prototheria — -pwTO(; — first;  Orjp — a  wild  beast. 
Ptychodont — 7tt6^ — a  fold,  as  in  the  molar  of  the  rabbit. 
Quadrituberctjlar — quatuor — four;  tuber — a  knob. 
Quinquetubercular — quinque,  five;  tuber — a  knob. 
Radul^ — rado,  radere — to  scrape. 
ScALPRiFORM — scalprufu — a  chisel,  as  in  the  rodents. 
Selenodont — (7s/.rjy/j  (the  Moon) — crescentic,  as  in  the  sheep  or  camel. 
Teratoma — rspai; — a  monster. 
Thecodont — d'/jx/j — a  sheath,  as  in  the  crocodile. 
Triconodont — tres,  tria — three;  xco)ju; — a  cone. 
Tritubercular — tres,  tria — three;  tuber — a  knob. 


APPENDIX 


NOTE   A 

A  Case  of  Hereditary  Absence  of  the  Crowns  of  the  Teeth 

The  following  extremely  rare  hereditary  dental  abnormality,  passing  through 
six  generations,  has  been  referred  to  in  Chapter  II. 

A.  H.,  aged  21  years  (February,  1910),  is  a  member  of  a  family  which  presents 
an  extraordinary  condition  of  the  teeth. 

The  Family  history  is  normal.  The  father,  aged  59  years,  a  cottager;  the  mother 
is  aged  57  years.  She  is  opharmotic — i.  e.,  has  an  open  bite — and  is  edentulous, 
except  for  the  first  right  maxillary  incisor,  which,  however,  is  loose.  It  has  no 
crown.  The  root  is  black,  shaped  on  its  surface  similarly  to  those  of  her  children. 
She  is  hypermetropic. 

All  the  members  of  the  family  are  somewhat  stunted  with  regard  to  their  height. 
The  hair  is  plentiful,  the  nails  normal,  the  skin  healthy  and  fine,  the  nervous 
system  probably  normal,  though  it  would  seem  that  the  youngest  son  and  the 
younger  daughter  are  inclined  to  be  mentally  defective.  A  Hampshire  family, 
living  in  a  rural  district  on  sandy  soil,  370  feet  above  the  sea  level,  where  the 
climate  is  dry  and  the  water  "soft,"  it  consists  of  parents,  two  daughters,  and 
five  sons,  of  whom  three. of  the  latter  are  married.    Brief  histories  are  as  follow: 

(i)  Henry,  aged  38  years,  living  with  wife  and  son  (2)  at  an  elevation  of  4S0 
feet  above  sea  level.  Climate  damp,  water  "soft."  All  the  twenty  anterior  teeth 
are  practically  on  the  same  plane  as  the  surface  of  the  gum.  The  maxillary  third 
molars  have  ill-developed  crowns;  the  right  mandibular  third  molar  has  a  natural 
crown  with  deep  fissures.  The  first  right  mandibular  molar  is  carious.  He  has 
had  four  maxillary  and  the  left  first  mandibular  molar  removed  on  account  of 
loosening,  not  "toothache." 

(2)  Henry,  junior,  son  of  (i),  aged  io|  years,  was  breast  fed.  The  tonsils  were 
removed  at  the  age  of  three  years.  There  were  no  infantile  diseases,  nor  any  facial 
deformity.  He  is  prosharmotic — i.  e.,  has  an  edge-to-edge  bite.  The  deciduous 
teeth  became  loose  and  were  shed.  Teeth  present:  Maxilla — all  incisors,  the  right 
canine  erupting,  the  first  molars  in  place,  but  having  no  crowns.     The  first  right 


358 


APPENDIX 


premolar  has  a  fairly-well  shaped  crown.     Mandible — the  incisors  have  flattened 
crowns,  the  deciduous  canines  are  still  present,  the  other  teeth  have  deficient 

crowns. 

Fig.  327  Fig.  328 


Plaster  casts  of  mouth  of  a  woman,  aged 
twenty-two  years.  X  to-  The  patient  was  the 
member  of  a  family  who  exhibited  for  six  suc- 
cessive generations  a  tendency  for  failure  of 
development  of  the  crowns  of  the  permanent 
teeth.  See  the  accompanying  text.  Three 
maxillary  molars  had  been  extracted  for  the 
relief  of  bi-antral  disease.  The  maxillary  third 
molars  and  the  right  mandibular  third  molar 
have  not  yet  erupted.  At  x  an  unerupted  hori- 
zontally placed  second  premolar.  The  third 
molars  in  this  patient  and  in  a  brother  and 
sister  possessed  fairly  well-developed  crowns. 


Plaster  casts  of  mouth  of  woman,  aged  thirty- 
six  years.  X  tV-  Sister  of  the  patient  of  the 
preceding  figure.  The  second  right  maxillary 
molar  and  the  second  left  mandibular  premolar 
and  first  molar  have  been  extracted  as  a  con- 
sequence of  dental  caries.  The  right  mandibular 
third  molar  is  not  yet  erupted. 


APPENDIX 


359 


(3)  Rose,  aged  36  years.     All  the  teeth  are  lacking  in  well-developed  crowns, 
except  the  left  mandibular  third  molar.     Appearances  similar  to  those  of  the 


Fig.  329 


Fig.  330 


Plaster  casts  of  mouth  of  a  man,  aged  thirty- 
eight  years.  X  ts-  Father  of  the  patient  of  the 
succeeding  figure.  The  mandibular  first  left  molar 
and  the  maxillary  first  and  second  molars  on  both 
sides  have  been  extracted  as  a  consequence  of  dis- 
ease. The  mandibular  right  first  and  second 
molars  are  carious. 


Plaster  casts  of  mouth  of  a  boy,  aged  ten 
and  a  half  years.  Son  of  the  patient  of  the 
preceding  figure.  X  tu-  The  maxillary 
right  premolar  is  probably  the  first. 


patient  Annie.    She  is  opharmotic,  and  caries  is  present  in  places.    She  has  never 
had  odontalgia.    She  is  hypermetropic,  and  wears  spectacles. 


360 


APPENDIX 


(4)  Archibald,  aged  19  years,  quick  and  intelligent,  has  the  appearance  of  being 
edentulous,  having  an  epharmotic  bite.  Teeth  are  all  levelled  with  the  surface  of 
the  gum. 

Fig.  331 


Plaster  casts  of  mouth  of  a  boy,  aged  nineteen 
years.  X  xo-  Brother  of  the  patient  of  the  suc- 
ceeding figure.  The  right  mandibular  first  molar 
and  the  left  second  premolar  and  first  molar  had 
been  extracted  as  a  consequence  of  dental  caries. 


Plaster  casts  of  mouth  of  boy,  aged  fifteen 
and  a  half  years.  X  tb-  The  maxillary 
second  left  premolar  has  not  erupted.  The 
right  first  molar  has  been  extracted. 


(5)  Ronald,  aged  15I  years,  probably  mentally  deficient.  All  the  teeth  have 
their  visible  portions  level  with  the  surface  of  the  gum,  except  the  right  maxillary 
second  premolar,  whose  crown  is  cusped  and  fissured.  He  is  opharmotic,  the 
alveolar  margins  being  8  mm.  apart  at  the  "incisive  spot." 

(6)  Sidney,  aged  30  years.    No  notes  at  present. 

(7)  Another  brother  living  in  America.    No  notes. 

(8)  The  patient,  Annie,  aged  21  years,  had  been  breast  fed,  had  had  measles 
and  bronchitis.     She  is  opharmotic.    Dental  History:    There  are  ten  maxillary  and 


APPENDIX 


361 


fourteen  mandibular  roots  present.  The  well-formed  left  mandibular  third  molar 
has  a  crown.  The  roots  have  polished  hard  brown  surfaces;  no  pulp  canals  visible, 
but  a  slight  depression  occurs  here  and  there.  There  are  no  traces  of  dental  caries 
nor  any  deciduous  roots  remaining.  An  a;-ray  photograph  showed  an  unerupted 
right  maxillary  second  molar  lying  horizontally  in  the  jaw,  with  its  crown  pressing 
on  the  root  of  the  first  premolar.  She  had  been  treated  for  bilateral  antral  disease. 
She  complained  (December  31,  1909)  of  a  vague  pain  in  the  first  premolar.  As  it 
was  functionless,  and  as  the  crown  of  the  second  premolar  was  touching  it,  it  was 
extracted  and  a  section  made.  This  showed  no  enamel,  and  appearances  in  the 
coronal  dentine  as  if  there  never  had  been  any  enamel  formed.  On  May  28,  1910, 
the  unerupted  premolar  was  extracted  because  it  appeared  to  be  keeping  up  the 
antral  disease.  This  tooth  possessed  Nasmyth's  membrane,  but  had  no  capsule. 
The  removal  of  the  tooth  was  followed  by  cessation  of  antral  pains  and  symptoms 
of  disease. 

The  above  description  does  not  at  all  pretend  to  be  complete.  The  patients 
are  being  watched,  and  the  cases  are  being  still  further  investigated  with  a  view 
to  further  and  fuller  publication. 

GENEALOGICAL    TREE 


/ 


(1)     I 

/ 
(2) 


(3)     (S) 


(r) 


X  =  Mavriarjo 
•  =  Affealed  male 
Q—Unaff'ected  female 


362 


APPENDIX 


NOTE   B 

The  Nervous  System  of  the  Dental  Pulp 

In  view  of  the  recent  observations  of  Mr.  Howard  Mummery,  on  whose 
authority  nerve  fibrils  enter  the  dentinal  tubules,  the  author  desires  to  record 
the  fact  that  he  has  been  able  to  stain  the  non-medullated  fibres,  in  the  pulp  by 
using  several  processes,  notably  those  of  Freund  and  Dogiel,  and  the  intra-vitam 
methylene-blue  methods. 

Fir,.  -,v. 


A  non-medullated  nerve  fibre  in  the  dental  pulp  of  man. 
Mr.  Douglas  Gabell. 


Photomicrograph  by 


It  is  easy  to  demonstrate  the  ■medullated  nerve  fibres.  Osmic  acid  shows  them. 
They  may  be  obtained  practically  unchanged  by  removing  a  permanent  misplaced 
canine  from  the  mouth  of  a  child  of  8  or  lo  years  (the  apex  being  unclosed)  with 
warm  forceps,  rapidly  wiping  off  the  blood,  and  placing  at  once  in  a  warmed  tube 
containing  a  2  per  cent,  solution  of  methylene  blue  in  physiological  salt  solution, 
kept  at  a  temperature  of  37°  Centigrade  for  30  minutes.  After  breaking  in  a  vice, 
the  pulp  is  removed  and  a  scraping  from  the  surface  of  the  dentine  is  mounted  in 
picro-glycerine.  The  non-medullated  nerves  may  be  rendered  apparent  by  obtaining 
a  young,  freshly  extracted  human  tooth — a  canine  for  choice,  carefully  crushing  it 
in  the  jaws  of  a  vice,  removing  the  pulp  with  a  needle  point,  laying  it  on  a  slide, 


APPENDIX 


3G3 


and  moistening  it  with  a  yV  per  cent,  solution  of  methylene  blue  in  physiological 
salt  solution.  In  four  hours  the  non-medullated  nerve  fibres  will  be  stained.  The 
process  must  be  watched,  as  overstaining  is  easy.  The  preparation  can  then  be 
mounted  in  picro-glycerine. 


Fig.  334 


Same  as  the  preceding.     X  '^y"- 
of  the  pulp. 


At  .T  the  fibre  branches  into  two  divisions.    A^  nuclei  of  cells 
Photomicrograph  by  Mr.  Douglas  Gabell. 


NOTE   C 


Oral  Electricity 

Electric. cells  are  frequently  formed  in  the  mouth,  metaUic  poles  being  present 
and  an  electrolyte  intervening.  The  greater  the  electro-positive  or  electro-negative 
the  metal  the  greater  the  electro-motive  force.  In  the  electrolytic  scale,  gold  is 
nearly  the  most  electro-negative  of  all  metals  placed  in  the  mouth,  while  aluminium 
is  the  most  electro-positive.  If,  therefore,  two  metals  of  different  electro-motive 
force  come  into  contact  or  almost  into  contact,  and  the  sahva  is  ionized  to  such  an 
extent  as  to  be  efficiently  electrolytic,  the  cathions,  or  —ions,  will  move  towards  the 
-I- pole  or  more  electro-positive  side,  while  the  anions,  or  4- ions,  will  move  towards 
the  —pole,  and  a  certain  amount  of  electricity  will  be  evolved. 

This  action  may  be  carried  to  a  greater  degree  than  is  usual  in  the  moulh. 


364  APPENDIX 

Clinically  this  force  becomes  more  manifested,  at  times,  under  certain  conditions, 
in  a  disastrous  manner.  Thus  a  i6-carat  gold  band  which  is  used  for  supporting  a 
denture,  if  attached  to  a  molar  tooth,  for  instance,  which  contains  a  large  amalgam 
filling,  may  in  these  cases  become  so  electrically  affected  as  to  break,  on  account  of 
the  molecular  changes  set  up  by  the  current,  and  the  filling  similarly  to  become 
disintegrated  and  ultimately  become  loosened. 

Mere  contact  of  a  metal  with  enamel  or  dentine  is  not  appreciated  by  the  pulp. 
It  is  when  two  dissimilar  metals  are  brought  into  contact,  separated  only  by  a  thin 
film  of  saliva,  which  acts  as  the  electrolyte,  and  the  circuit  is  completed,  that 
voltaic  currents  are  set  up — as  for  instance  when  the  metal  ring  of  a  small  mirror 
touches  the  surface  of  a  gold  or  an  amalgam  filling.  This,  of  course,  constantly 
takes  place  during  operations,  and  is  as  a  rule  unnoticed  by  the  patient,  on  account 
of  its  extremely  light  character;  but,  at  times,  the  pulp,  stimulated  by  the  electrical 
action,  responds  by  a  sudden  spasm  of  acute  neuralgic  pain. 


INDEX 


Aard-vark,  dentition  of,  88,  89,  300,  345 

Absence  of  crowns  of  teeth,  hereditary,  357 

Absorption  of  teeth,  physiological,  130 

Abyssinia,  diet  in,  39 

Acrodont  anchylosis,  127 

Acromegaly,  289,  290 

Adaptive  medication  of  organs,  93 

Age  changes  in  mandible,  277 

in  maxillae,  268 

in  teeth,  226 
Aglypha  colubrine  snakes,  95 
Albrecht  on  development  of  premaxillary  bones, 

75 
Alepidosaurus  ferox,  dentition  of,  129 
Alveolar  point,  232 

processes  of  jaws,  251 
Alveolo-labial  sulcus,  230 
Ambylopsis,  eyes  of,  93 
Amphilestes,  139 
Analogy,  134 

Anarrhicas  lupus,  dentition  of,  34,  84 
Anatomy  of  teeth,  174 
Ancestors  of  horse,  336 

of  whales,  117 
Anchylosis,  126 
Angle,  facial,  171 
Angular  bone,  69 

centre,  274 
Annamese,  teeth  of,  46 
Ant-eater,  dentition  of,  343,  344 
Antelope,  dentition  of,  343 
Anthropoidea,  147 
Antrum  of  Highmore,  232,  267 
Archetype  theory,  93 
Armadillo,  dentition  of,  344 
Artery,  inferior  dental  (mandibular),  247 

internal  maxillary,  247 

posterior  dental,  247 
Articular  centre,  274 


Articulation  positions,  44,  45 
Artiodactyla,  337 
Attachment,  bone  of,  125,  126 
Atypical  dental  heredity,  no,  357 
Aye-aye,  dentition  of,  148 


Badger,  teeth  of,  323 

BalcEnidce,  73,  328 

Batistes,  incisors  of,  57 

Bateson  on  variations  of  teeth,  109 

BathyergidcB,  318 

Bdellosloma,  teeth  of,  64 

"Beaked  whales,"  dentition  of,  328 

Bear,  dentition  of,  322 

Beaver,  dentition  of,  318 

Belgium,  diet  in,  35 

Betelnut,  chewing  of,  38 

Bhils,  mimicry  of,  115 

Birdwood  on  food  of  Hindus,  37 

Bison,  dentition  of,  343. 

Black  on  measurements  of  teeth,  180 

on  permanent  maxillary  molars,  198 
Bland-Sutton  on  cervical  teeth,  30 

on  development  of  mandible,  272 

on  teratomatous  teeth,  31 
Blood  pressure  theory  of  eruption,  292 
Boar,  dentition  of,  58,  338 
Bone  of  attachment,  125,  126 
Bovidce,  343 
BradypodidcE,  344 
Bradypus,  dentition  of,  345 
Brooke  NichoUs  on  ornithorhynchus,  353 
Broomell  on  einiption  of  teeth,  294 
Briicke's  articulation  positions,  45 
Buccinator  muscle,  231 
Buffalo,  dentition  of,  343 
Bushmen,  diet  of,  40 


366 


INDEX 


Calcified  teeth,  31 
Camel,  dentition  of,  340 
CanidcB,  320 
Canines,  anatomy  of,  182 

definition  of,  92 
CantelidcE,  316 
Carcharias,  teeth  of,  87,  128 
Caries,  races  immune  from,  42 
Carnassial  teeth,  90 
Carnivora,  320 

Carnivorous  type  of  dentition,  286 
Casiorida,  318 
Catarrhini,  149 
Catastrophic  theory,  104 
Celtic  race,  168 
Cementum,  functions  of,  304 
Centres  of  ossification  of  jaws,  267,  271 
Cephalophus,  343 
Ceratodus,  64,  137 
CercopithecidcE,  147 
Cerebral  capacities,  various,  x68 

vesicles,  263 
Cervical  glands,  248 

teeth  of  sheep,  Bland-Sutton  on,  30 
CervidcB,  340 
Celacea,  327 
Chsetodonts,  59 
Chamois,  119,  343 
Cheirotnys,  148 
Cheiroptera,  314 
Chevrotains,  340 
China,  diet  in,  36 
ChinchillidcE,  318 
Chiselling,  function  of,  57 
CholxBpus,  345 
Chorda  dorsalis,  263 
Cingulum,  91 
Civets,  322 

Cleft  palate,  Albrecht  on,  75 
Colubrine  snakes,  95 
Combat  as  a  dental  function,  53 
Combing  fur,  teeth  used  for,  56 
Comminution  of  food,  29 
Concrescence  theory,  136 
Condyle  of  jaw,  274 
Conical  teeth,  84 
Consonants,  production  of,  45 
Corneous  teeth,  31 
Coronoid  process  of  jaw,  274 


Correspondence  with  environment,  108 
Cranial  capacities,  various,  1 58 
Crocodile,  teeth  of,  88 
Ctenodaciylidce,  318 
Cuvier  on  origin  of  species,  104 


D 


Darwin  on  expression  of  emotions,  51 

on  origin  of  species,  103 
Darwinian  theory,  106 
Dasyure,  350 
Dasyuridm,  347 
DasypodidcE,  344 
DasyproctidcE,  318 
Death,  definition  of,  108 
Deciduous  teeth  of  man,  222 
growth  of,  278 
Definitions  of  teeth,  29 
individual,  98 
Dental  formulae,  98 

homologies,  132 

index,  168 

morphologies,  84 

notations,  73 

numeration,  63 

pain,  312 

pulp,  302 
Dentary  bone,  69 

centre,  273,  274 
Dentine,  functions  of,  301 
Dents  en  brasses,  65,  84 

en  caries,  64,  65,  84 

en  velours,  59,  65,  84 
Dentitions,  descriptions  of  various  forms  of,  166 
Deposition  of  bone  theory,  292 
Derivation  of  species,  proofs  of,  118 
Desmodus,  315 

Development  of  mandible,  Bland-Sutton  on,  272 
Diastema,  169,  336 
DicotylidcE,  340 
Di-enharmosis,  240 
Di-epharmosis,  241 
Diet  in  Abyssinia,  39 

in  America,  40 

in  Belgium,  35 

of  Bushmen,  40 

in  Ceylon,  39 

in  China,  36 

in  Denmark,  35 


INDEX 


367 


Diet  in  Egypt,  40 

in  Greece,  35 

in  Iceland,  36 

in  India,  37 

in  Italy,  36 

of  Maoris,  41 

of  Mexicans,  41 

in  Netlierlands,  36 

in  Persia,  38 

in  Roumania,  36 

in  Spain,  36 

in  Sweden,  36 
Dipodidce,  318 
Diprotodonts,  347 
Diphyodont  dentition,  166 
Disharmosis,  240 
Dissacus,  143 
Dominants,  121 
Dromotherhim,  138 
Duckworth  on  diastema  in  man,  16 
Dugong,  301,  329 

on  ethnic  mutilations,  46 
Duplicidentata,  dentition  of,  319 


Echidna,  71,  353 

Edentata,  343 

Egypt,  diet  in,  40 

Elaphodus,  341 

Elephant,  dentition  of,  332 

Elephas  imperator,  56 

Elliott  on  warfare  amongst  seals,  325 

EmballonuridcB,  314 

Emotional  expressions,  51 

Enamel,  functions  of,  299 

Endognathion,  77 

Enharmosis,  240 

Entocone,  140 

Environment,  correspondence  with,  ic 

Epharmosis,  240 

"Epithelial  theory"  of  eruption,  293 

Erinaceidce,  316 

Eruption  of  teeth,  dates  of,  295 

theories  of,  291 
Esquimaux,  diet  of,  40 
Ethnic  customs,  46 
mutilations,  46 

Duckworth  on,  46 
Exognathion,  77 


Facial  angle,  171 

Falero  on  teeth  of  Mexicans,  41 

Fang  of  viper,  55,  61 

Fawcett  on  development  of  jaws,  275 

Felidm,  321 

Fijians,  diet  of,  41 

Filing  of  teeth,  46,  47 

Fishes,  teeth  of,  34,  63,  84,  125,  128 

Fissipedia,  320 

Food  of  fishes,  34 

of  mammals,  35 

of  man,  35 

of  reptiles,  35 
Foramen  magnum,  168,  172 
Formula,  dental,  74 
FrcBnum  labii,  230 

lingua,  230 
Functions  of  cementum,  304 

of  dental  tissues,  298 

of  dentine,  301 

of  enamel,  299 

of  gum,  305 

of  Nasmyth's  membrane,  298 

of  periodontal  membrane,  304 

of  pulp,  302 

of  teeth,  33 


Galeopithecid^,  316 
Caleopithecus  volans,  56,  134,  317 
Galley  Hill  man,  Keith  on,  156 
Ganglion  of  Bochdalek,  242 

of  Valentin,  241,  242 
Gaslrceia  theorie  of  development,  303 
Gazelle,  dentition  of,  343 
General  functions  of  teeth,  33 
CeomyidcB,  318 
Germ-layer  theory,  303 
Gingival  region,  250 

trough,  257 
Gingtymo-arthrodial  articulation,  166 
Giraffe,  teeth  of,  342 
GliridcE,  318 
Glossary,  355 
Gnathic  index,  172 
Goethe  on  origin  of  species,  106 
Gomphosis,  fibrous,  126 

osseous,  126 


368 


INDEX 


Greece,  diet  in,  35 
Growth  of  permanent  teeth,  283 
Gubernaculum,  283,  294 
Gums,  functions  of,  257 
Gutzmann  on  speech,  46 


Hapalid^,  147 
Haplodontidm,  318 
Hare,  319 

Heidelberg  jaw,  Keith  on,  162 
Schoetensack  on,  154 
Hemiramphus,  63 
Herbivorous  type  of  dentition,  99 
Hereditary  absence  of  crowns  of  teeth,  357 
Heredity,  no 
Heterodont  types,  74 
HeteromyidcE,  318 
Highmore,  Antrum  of,  232,  267 
Hindus,  customs  of,  37,  38 
Homalodontotherium   teeth  of,  75 
Homodont  types,  88 
Homology,  lateral,  133 

radial,  133 

vertical,  133 
Homo  sapiens,  162 
Horse,  ancestors  of,  336 

molars  of,  336 
Hewitt  on  dental  mutilations,  48 
Human  evolution,  152 
Huxley  on  origin  of  species,  107 
Hyaena,  teeth  of,  322 
Hycenidce,  320 
Hydromys,  319 
Hyoid  area,  245 
Hypocone,  140 
Hyracoidea,  332 
Hyrax,  dentition  of,  333 
HystricidcB,  318 
Hystricomorpha,  318 


Iberian  race,  168 

Implantation  of  teeth  by  anchylosis,  125,  127 

by  bone  of  attachment,  125,  126 

by  gomphosis,  126 

by  socket,  127 
Incisive  pad,  232 


Incisors,  deciduous,  of  man,  223 
definition  of,  92 
permanent,  of  man,  176 

Incomplete  evolution,  75 

Index,  dental,  i58 
gnathic,  172 

India,  diet  in,  37 

Infra-vomerine  centre,  268 

Insectivora,  316 

Insectivorous  type  of  dentition,  100 

Interstitial  growth  of  bone,  292 

Invertebrates,  teeth  of,  32 

Ipswich  man,  jaws  of,  157 

Isthmus  fauciictn,  229 

Iter  dentis,  288 


James  on  eruption  of  teeth,  293 

Japha  on  protective  mimicry  of  insects,  114 

Jaws,  development  of,  Fawcett  on,  275 

Low  on,  276 
Jeittles  on  origin  of  dog,  in 
Johnstone  on  whales,  72 


K 

Kangaroo,  dentition  of,  97,  348 
Keith  on  eruption  of  teeth,  290 

on  evolution  of  man,  160 

on  prehistoric  man,  160 
Kellicott  on  survival  of  fittest  in  toads,  112 
von  Klaatsch  on  origin  of  bone,  303 
Koala,  teeth  of,  349 
Korschalt  on  germ-layer  theory,  303 
Kubus,  170 
Kudu,  343 


Lagomyid^,  319 

Lamarck  on  origin  of  species,  104 

Lamna,  86 

Lamprey,  34 

Lang  on  ethnic  mutilations,  48 

Laporida,  319 

Lateral  homology,  133 

Lemur,  teeth  of,  148 

Life,  definition  of,  108 

Ligurian  race,  168 


INDEX 


369 


Linnaeus  on  origin  of  species,  104 
Lophitis  piscatorius,  94 
Low  on  development  o£  jaws,  276 
Lydelcker  on  Anthropoidea,  151 
Lympliatics,  deep  cervical,  248 
internal  maxillary,  248 
superficial  cervical,  248 


M 


MACH.?iRODONTID/E,  32 1 

Macrocephalic  races,  l68 
Macropodida,  347 
Macroscelidm,  316 
Magian  race,  168 
Malagasi,  diet  of,  40 
Mammals,  teeth  of,  314 
Mammalian  dentition,  typical,  66 
Mammoth,  Siberian,  55 

Texan,  56 
Man,  evolution  of,  152 

prehistoric,  152 
Manatee,  300,  329 
ManatidcB,  329 
Mandible,  changes  in,  226,  277 

development  of,  270 
Mandibular  area,  244 
canine,  208 
centre,  271 

deciduous  teeth,  224,  225 
incisor,  204,  207 
molar,  215,  218,  220 
premolar,  211,  213 
Manid(E,  344 
Maoris,  diet  of,  41 

Marett  Tims  on  concrescence  theory,  137 
Marshall  on  eruption,  295 
Marsttpialia,  346 
Masseter  muscle,  231 
Maxilla,  changes  in,  226,  268 
Maxillary,  area,  244 
canine,  182,  183 
incisor,  176,  177,  180 
molar,  192,  199,  201 
premolar,  186,  190 
Meckel's  cartilage,  272-277 
Megacheiroptera,  314 
Megadont  type  of  dentition,  167 
Meles,  323 

Mendelian  theory,  120 
24 


Mental  area,  244,  245 
Mento-Meekehan  centre,  271 
Merism,  109 

Mesognathous  races,  172 
Mesonix,  143,  144 
Mesoplodon,  66 
Metacone,  140 
Mexicans,  teeth  of,  47,  79 
Microcephalic  races,  168 
Microcheiroptera,  teeth  of,  314 
Microdont  races,  167 
Microlestes,  137 
Mimicry,  protective,  115 
Molars  of  man,  deciduous,  223 

permanent,  192,  215 
Mole,  dental  formula  of,  135,  317 
Monk  seal,  326 
Monophyodont  dentition,  166 
Monolremata,  teeth  of,  352 
Morphology  of  teeth,  84 

Moschus  moschiferous,  sexual  canines  of,  54,  340 
Mousterian  relics,  156 
Mummery,  Howard,  on  nerves  of  dental  pulp, 

308 
Muntjac,  teeth  of,  341 
MuridcR,  318 
Musk-deer,  53,  54,  340 

ox,  343 
MustelidcE,  320 
Mutability  of  species,  1 1 1 
Mutation  theory,  120 
Mutilations,  ethnic,  46,  50 
Myliobalis,  shapes  of  teeth  of,  70,  85 
Myrmecobitis,  350 
Mystacoceti,  whalebone  of,  72,  328 
Myxine,  teeth  of,  31,  64,  70 


N 

Narwhal,  53 
Nasal  centre,  268 

fossa,  primary,  264 
tooth  in,  22 
Naso-labial  area,  243 
Nasmyth's  membrane,  functions  of,  298 
National  diets,  35 
Natural  selection,  106 
Neanderthal  skull,  154 
Negroes,  diet  of,  40 
Neo-Lamarekians,  105 


370 


INDEX 


Nerve  fibres  in  dental  pulp,  307,  362 
Nerves,  inferior  dental  (mandibular),  242 

middle  superior  dental,  241 

naso-palatine,  242 

superior  maxillary,  242 
Newton  on  edible  birds'  nests,  37 
Notations,  dental,  73 
Notochord,  263 
Notoryctes,  351 
Notoryctida,  347 
Numeration  of  teeth,  63 
Nutrition,  influence  of,  on  eruption,  295 
Nycteridm,  314 


Oblique  succession,  128 

OctodontidcE,  318 

Occlusion  of  teeth,  233 

Odontalgia,  247,  310 

Odontoblasts,  function  of,  24,  302 

Odontoceii,  teeth  of,  73,  328 

Offence,  teeth  as  weapons  of,  55 

Omnivorous  type  of  dentition,  102 

Opharmosis,  240 

Opisthoglypha  colubrine  snakes,  95 

Opossum,  dentition  of,  350 

Oral  electricity,  363 

Orang-outang,  149 

Origin  of  species,  Cuvier  on,  104 

Darwin  on,  106 

Huxley  on,  107 

Lamarck  on,  104 

Linnaeus  on,  104 

Wallace  on,  123 
Ornamentation,  teeth  used  for  purposes  of,  46 
Ornitlwrhynchus ,  Brooke  Nicholls  on,  353 

dentition  of,  31 
Orbicularis  oris,  231 
Orbito-nasal  centre,  267 
Orthognathous  races,  172 
Orycteropodidm,  344 
Ossification  of  jaws,  267 
OtariidcB,  320 
Otocyon  megalotis,  74 
Ovarian  teratomata,  30 
Oxen,  teeth  of,  340 
Oysters,  57,  58 


Pain,  dental,  312 

Palate,  231 

Pangolin,  344,  345 

Papilla  palatina,  232 

Paracone,  140 

Paraconid,  141 

Parotid  gland,  230 

Patagonians,  diet  of,  41 

Peccary,  dentition  of,  340 

Pecora,  340 

Pectiniform  teeth,  90 

Pedelidm,  318 

Peramelida,  347 

Periodontal  membrane,  functions  of,  304 

Perissodactyle  ungulates,  teeth  of,  333 

Permanent  teeth  of  man,  174 

age  changes  in,  226 
Phalanger,  teeth  of,  348 
PhalangerincB,  347 
PhascolarclincB,  347 
PhascolomynidiB,  347 
PhocidcE,  320 
Phyllostomatidcz,  314 
PhyseteridcB,  328 

Pickerill  on  immune  races  of  mankind,  42 
Pig,  338 
Pike,  52,  126 
Pinnipedia,  325 
Pithecanthropus  erectus,  155 
Pitts  on  eruption  of  teeth,  288 
Pituitary  body,  289 
Placodus,  85 
Plata?iistidce,  328 
Platyrrhini,  148 
Pleurodont  anchylosis,  127 
Pogonias,  molariform  teeth  of,  59 
Poison  fang  of  snakes,  55,  61,  95 
Polyergus,  34 
Polyphyodont,  128 
Polyprotodont,  347 
Polyzoa,  303 
Porcupine,  teeth  of,  318 
Post-oral  cleft,  264 
Potamogalidm,  316 
PoteroincB,  347 
Pre-canine,  76 
Prehension  of  food,  52 
Prehistoric  man,  Keith  on,  160 
PremaxiUary  bone,  95,  269 


INDEX 


371 


Premaxillary  centre,  268 
Premolars,  98,  186,  211 
Pre-oral  cleft,  264 
Primary  nasal  fossa,  264 
Primates,  teeth  of,  146 
Pristis,  extra-oral  teeth  of,  59,  126 
Proboscidea,  331 
Processus  lateralis,  270 

medialis,  270 
Procyonidce,  320 
Prognathism,  169 
Pronghorn,  dentition  of,  342 
Prosharmosis,  240 
Protochorda,  304 
Protective  colouration,  173 

mimicry,  115 
Proteroglypha  colubrine  snakes,  95 
Protocone,  140 
Protoconid,  141 
Pleropidcs,  314 
Pulp,  functions  of  dental,  302 


Raccoon,  dentition  of,  324 

Radial  homology,  133 

RadulcB  of  invertebrates,  32,  33 

Recessives,  121 

Redier  on  absorption  of  teeth,  131 

Reichardt  on  the  Mousterian  skull,  156 

Remian  race,  168 

Reptiles,  teeth  of,  35,  65,  88,  127,  129 

Rhinoceros,  teeth  of,  331,  333,  337 

RhinolophyidcE,  314 

Rhytina,  330 

"Right"  whales,  327 

Riina  oris,  229 

Rostral  teeth  of  sawfish,  59 


Salivary  glands,  230 

Salter  on  oral  production  of  speech,  42 

Sarcophilus,  350 

Sargus,  84,  126 

Schoetensack  on  Heidelberg  jaw,  154 

Schroeder  on  Mendelian  law,  121 

SciuridcB,  318 

Scott  on  evolution  of  mammalian  crowns,  143 

Sea  otter,  324 . 


Seals,  326 

eared,  325 
Selection,  natural,  106 

sexual,  107 
Selenodont  dentition,  340 
Sensations,  modifications  of,  312 
Sensitiveness  of  cementum,  310 

of  dentine,  307 

of  enamel,  306 
Serial  homology,  133 
Sexual  selection,  107 

warfare,  teeth  used  in,  53 
Sheep,  teeth  of,  343 
Shrew,  teeth  of,  316 
Sieves,  teeth  used  as,  59 
Sigmoid  notch  of  mandible,  teeth  in,  22 
SimiidcB,  dentitions  of,  147 
Simplicidenlaia,  teeth  of,  318 
Sirenia,  329 

Skull  of  fish,  bones  of,  69 
Sloth,  teeth  of,  344 

Smurthwaite  on  races  of  mankind,  168 
Snakes,  teeth  of,  55 
Solenodontid(B,  316 
Soricidce,  316 
SpalacidcB,  318 
Spalacotherium,  139 
Species,  derivation  of,  118 

mutability  of,  ill 

origin  of,  103 
Specific  major  functions  of  teeth,  42 
Speech,  mechanism  of   oral   production  of,  42 

46 
Sperm  whale,  328 
Sphenodon,  61,  137 
Sphenomaxillary  fossa,  241 
Splenial  centre,  271 
Spontaneous  generation,  104 
Spy,  man  of,  155 
Squalodonlidce,  328 
Squirrel,  318 
Stenson's  duct,  232 
SubHngual  gland,  230 
Submaxillary  gland,  230 
Substitutes  for  teeth,  60 
Succession  of  teeth,  oblique,  128 

vertical,  128 
Sumner  on  patterns  of  skins  of  fishes,  113 
Surangular  centre,  274 
Survival  of  fittest,  113 
Sus  babiriissa,  teeth  of,  339 


372 


INDEX 


Talpid^,  316 

Tapir,  teeth  of,  333 

Tarsipedince,  347 

Tarsipes,  347,  350 

Temporal  area,  243 

Teratomatous  cysts,  teeth  in,  Bland-Sutton  on, 

30.  31 
Tetradon,  jaws  of,  85 
Teutonic  race,  168 
Theory,  concrescence,  136 

Darwinian,  103 

germ-layer,  303 

Mendelian,  120 

mutation,  120 

tritubercular,  138 
Thecodont  dentition,  127 

Thomas  Oldfield  on  teeth  of  ornithorhynchus,  353 
Thylacine,  350 
Tilbury  skull,  157 
Tomes  on  eruption  of  teeth,  288 

on  odontoblasts,  24 

on  teeth  of  walrus,  326 
Toxotes  jaculator,  59 
Trabecules  cranii,  264 
Tragulus,  340 

Transport,  teeth  used  for  purposes  of,  54 
Trichechidce,  320 
Tricodont  teeth,  139 
Trigla,  94 
"Trigon, "  140 
Tritubercular  theory,  138 
TupaiidcE,  316 

Turner  on  dental  heredity,  no 
Turner,  Sir  William,  on  precanine,  77 
Tyrpharmosis,  240 


U 


Ungulata,  331 
Ungulates,  artiodactyle,  337 
perissodactyle,  333 


Valez  on  kubus,  170 

Vampire  bat,  315 

Varanus  niloticus,  teeth  of,  65,  127,  302 

Variations  morphological,  84 

in  number  of  canines,  77 

of  incisors,  76 

of  premolars,  78 

of  molars,  78 
of  teeth,  Bateson  on,  109 
Veddas,  food  of,  39 
Vertical  homology,  133 

succession,  128 
Vesicles,  cerebral,  263 
Vespertilionidcs,  314 
Vestibulum  oris,  231 
ViverridcE,  320 
de  Vries  on  mutation  theory,  120 


W 


Wagogo  tribes,  mutilations  of  teeth,  46 
Wallace,  Russell,  on  Mendelian  theory,  123 
Walrus,  teeth  of,  54,  326 
Water  deer,  342 

Weapons  of  offence,  teeth  used  as,  55 
Weissmann  on  variation  of  species,  no 
Whalebone,  72 
Whales,  ancestors  of,  117 
dentition  of,  72,  327 
Wharton's  duct,  232 
Wombat,  dentition  of,  349 
Wortman  on  trituberculisrri,  142 


Zeuglodontid^,  328 
Zygomatic  centre,  267 


1          Date  Due 

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